There is a fairly wide spread belief within the Aikido community that all joint locks and some throws (or rather their break falls) are harmful to children. I am looking for actual evidence-based medicine research(1) on the medium to long term harm to the development of children's body. Adults can practice these locks for decades without any adverse effects as their bones, tendons, and so on are all finalised. On the other hand, kids bodies are still growing and might be much weaker to resist strain. That's the common view within the Aikido teaching world. I am looking for actual medical evidence of such.
For example, here are two common locks used in Aikido: kote gaeshi (supinating wristlock) and kote hineri (rotational wristlock). The former twists the write anti-clockwise, the latter clockwise if applied to the left hand.
Both can be very painful in the short term but once the lock is released the pain disappears. The goal of locks is to either cause the body to move in a predefined way (to set up for a throw) or to pin the target so they are disinclined to resist the pin. The locks are safe to practice on adults: they do not cause any short, medium, or long term damage if applied correctly. Of course, they could do grievous damage if applied in haste on unsuspecting targets. But damage is not the goal. Otherwise, we could not train! To be fair, pain is not the goal either.
(1) Answers based on either anecdotal evidence or hear say will attract down votes.