It is safe to give a kitten cooked chicken as a treat. The chicken should be cooked without any seasonings and should have the skin removed to avoid providing any excess fat in the kitten's diet.
It is also important to remove the chicken from the bones prior to serving it to the kitten. Kittens may choke on the bone, and chicken bones become quite brittle and shard easily after being cooked.
Be sure to cut the pieces small enough that they can be chewed up easily by the kitten.
This treat should only be fed to kittens once or twice per week and should be omitted from their diet if it causes an upset stomach.