We are in a world very similar to ours. But, one day, 1% of the children that are turning 10 are gaining super strength (this is an ongoing process : from that date, all the children under 10 may potentially obtain that super strength at their 10th birthday). This phenomenon is roughly evenly distributed geographically, so no country really has a higher share of these children compared to their population.
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). It isn't lost as they age and grows at the same proportion the strength of a normal child would. The muscle mass isn't increased and there are no apparent changes to their body.
Governments of the world, after initial analysis of this phenomenon, decided it would be better to know exactly which kid has super strength and which kid doesn't. They enacted new laws requiring that children on their tenth birthday submit themselves to testing, and the results of that test are put on a special global database, so people can know if necessary if they have super strength or not. Not having done that test is grounds for arrest and being forced to perform 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.
Is there a way to be certain that the kids are giving their all at the test, or is there a physical test where strength can be determined regardless of if the kid is trying to dissimulate their super strength?