is there a physical test where strength can be determined regardless of if the kid is trying to dissimulate their super strength?

You know that test doctors do, in which they hit you sligjtly below the kneecap with a little hammer to test a reflex?

Do it with their legs tied to something heavy.

Or have them punch a punching bag... It's not hard to see whether someone is pulling their punches.

1. Children of that age are naive about many things. A trained 'nice cop - nasty cop' setup would easily trip them up. Once they've admitted it verbally (and they will certainly know) getting them to give a demonstration is easy.




2. Even more unethical method - Isolate them from their parents and say they will never see them again unless they can escape. If they can break free then they have the strength. If they can't then they will show increasing distress and the test can stop. (I wish I hadn't thought of this, it's reminiscent of Dr Mengele)




3. Find out what they really want for Christmas (other religions and customs may apply) and tempt them with it if they'll demonstrate their abilities.

Make it so they want to be detected. Give the strongest special status and high honours and all the nice things in life. Have special sporting leagues featuring the super strong competing for hordes of devoted fans.

Basically make it so people want to prove they are as strong as possible, rather than trying to hide it.

Tests that depend on surprise or reflex, not conscious action. Also of benefit is that kids tend to have poor decision making skills, which means it's easy to make them forget instructions to cheat.

For instance, get them playing a physical game, informing them it's just to give them something to do after the tests are done (which are normal, boring tests that could be faked), and that doing well awards them some prize that a 10 year old would want. Then you very subtly start ramping up the difficulty which, if they're invested in the game, they'll unconsciously compensate for. Say, playing a version of dodgeball against an automated cannon, where they have to avoid getting hit by the ball but in turn have to knock over targets to "win" by beating the cannon. You start off with the cannon tracking and firing at speeds a normal kid would be expected to have a chance against and targets that don't require much force to knock over, then slowly ramp up the difficulty.

It's incredibly hard to fake being less physically proficient than you are. Ask a fast runner to look like they're running as fast as they can, but pretend they're slower than they really are; it's a hard thing to do. An example that comes to mind is the Deep Space Nine episode "Take Me Out to the Holosuite". Max Grodénchik, who played Rom, considered a career in pro baseball before going into acting, but Rom was supposed to be the most inept player on the DS9 team, and Grodénchik found it impossible to play that badly. He ended up having to play leftie (throwing, batting, and catching) in order to look realistically bad.

A kid is going to have an even worse time trying to fake it.

"The main problem is the test itself. There is no other way to detect
these "super kids" than measuring their strength/speed/stamina etc.
but the governments are worried that parents may instruct kids to fake
a lower strength and avoid registration as a person with super
strength."

"No way"? These children attend school surely? A very normal part of your schooling is gym/recess and so on. It should not be at all hard to notice some 10 year-old punting a football over the school or possessing a seven foot vertical leap. Have your recess monitors and gym teachers actually pay attention- problem solved and without taxpayers having to fork over more money to detect superhumans. Gym has grades to measure exactly how you compare to everyone else physically- as part of a bog-standard schooling experience. This is not something that's going to be hidden- especially not by kids who aren't even teens.

If your population is determined to keep the super-strength hidden, use knee reflect test as @Renan suggested, or attach electrodes to a muscle in the body, and zap them with a small amount of electricity to cause involuntary motion. Or several different muscles, stimulated in random order to make faking harder. As a final step, you can sedate kids, but it is a lot of effort to do safely, and kinda boring.

Also, they can do medical test for something in body's biology that is the source (or consequence) of strength: increased adrenalin, higher muscle density, stronger bones or tendons (to handle super-muscles)

"Surpize" tests will not work as population will learn about all of them soon enough.

But, Social Enginnering offers easy ways to ensure that people openly reveal their strength.

1. Tell your population that enemy countries use their super-strong people as soldiers, so yours needs to defend itself. Make your own super-strong soldiers heroes to the public (like sports stars in US). You do not even have to pay them that much, they might get enough money from product endorsements or simply donations. Can you imagine a teen that does not want that for themselves?




2. Even if you lock supers up and experiment on them, tell people that uncontrolled super-strength is dangerous, both to super and those around them. Spread viral videos of accidents involving unexperienced supers. The official PR campaign is that testing is a responsible and caring thing to do; also encourage "if you see something, say something"; what if that super accidentally hurts you, or your g/f?

School sports day

I don't know how common this is these days, but in primary school we used to have an annual sports day. Mostly races, maybe with a sack race or an egg and spoon race. Standing long jump. Bean bag tossing. Simple activities that any child can take part in without risk of anything worse than a grazed knee.

Kids like to win races, and it's going to be very hard for a child of that age to resist throwing the bean bag further than all their peers when placed in a simple competitive situation, they don't have the self control of an adult. All you have to do is observe, and hand out prizes.

Children are greedy.

Give them as much chocolate / toy cars / whatever they desire most as they can carry. Then measure the weight as they leave the room.

You want to measure physical strength? There's a really straightforward dystopian answer here, surprising that no one has mentioned this one yet

Battle Royale

As per the novel and movie of the same name. Pick or create an uninhabited area that will be completely cut off from the outside world through a full military blockade. Take all the 10 year olds to this area and remove all forms of contact with anyone else, especially their parents. Now tell them that the last man(child?) standing gets to go home. You can provide additional motivation through means like exploding collars, if need be. A simple fight to the death(or the appearance of such) should reveal any "talented" children quickly enough.

Play with them.

I've played with kids and once they're really playing, they won't have the mental focus to pull punches.

I've made them push against me with their hands. In fact, as a 20 yr old guy, I was able to hold off two 10 yr old boys with one hand each, and have lots of strength to spare. I can easily push the two boys across the room.

If one of them can make me struggle, then I know there's something wrong.

offer candy to any kid that can lift the barbell. it's not that complicated.

as long as there is no punishment for the supers, there is no disinclination on their, or their parents account, at demonstrating their prowess.

the actual complication comes in interactions between supers with their non-super peer group, since kids are generally mean, selfish, impulsive and just generally nasty.

in which case, the supers may need to be segregated, which then drives the motive to secrecy. that's good drama right there.

Skeletal muscles can be engaged using electrical muscle stimulation (EMS). EMS has been featured in several studies on the effects of preserving strength in those suffering from Intensive Care Unit acquired weakness (ICU-AW). A similar application could be used to manually stimulate the child's muscle ensuring that they cannot suppress their own strength.

I might suggest that the most accurate way to measure their strength would be to engineer a force measuring device that could fit in their hand and applying EMS electrodes to their forearm to measure their grip strength.

The benefits of testing this way would be that the test can be done quickly, safely and measured non-subjectively. The EMS kit and force measuring device would also be fairly easy to move about as well.

This super strength can range from having the strength of a strong adult male (for most of them) to truly ridiculous feats like being able to punch through walls and run hours at 50 km/h without being tired (extremely rare).

You're actually describing two slightly different things there: Enhanced muscle power and increased muscle stamina. Both of these are relatively easy to test for, but require slightly different methods.

As Renan and Bald Bear already pointed out, involuntary muscle contractions can be triggered by stimulating the right nerves -- either electrically or with a mallet. The resulting force is easy to measure, the test subject has no control over it, and it's perfectly safe.

Endurance can also be measured in a number of ways that are hard to fake. For example, have the kid run full-tilt for a set amount of time -- I imagine 10 minutes or so would probably be sufficient. A normal child will show an increased heart rate when engaging in this activity. A powered child will show no significant increase in heart rate until they reach speeds a normal child wouldn't even be capable of -- so either they reach those speeds and you know, or they try to hide it by sticking to normal speeds, but then their heart rate doesn't increase like a normal kid's would, so you still know.

Like the previous method, heart rate is easy to measure, the test subject has no direct control over it, and it's perfectly safe. If their parents were really determined to keep their abilities secret, there are ways increased heart rate could be induced, but assuming both resting heart rate and active heart rate are measured and compared against known typical ranges, it would be extraordinarily difficult to administer a drug and get the timing just right to ensure their heart rate looks normal both at rest and when active.

Finally, there are ways to measure muscle fatigue more directly, using electromyography (EMG), or based on biochemistry such as amounts of lactate, muscle glycogen, changes in pH, etc. Any of these would be difficult to fake, though the biochemical tests have the minor drawback of being slightly more invasive -- they are probably the only option discussed here that would require a sample taken by needle. Still, they should be perfectly safe and cause minimal pain.