These are generally scripts which are aimed primarily at performance by a school-age cast. This includes children playing children's roles and children playing adult roles.
There is a wide variety, including small cast plays and whole class (or even whole school!) pieces.
The fact that they were originally designed for children hasn't stopped some of the scripts - particularly the rhyming scripts and the pantomimes - being played by adult casts, therefore treat this categorisation with caution!
Many of the scripts written for adults are well within the grasp of teenagers, therefore if you are aiming at a specific age-group, then it may be better to search by Minimum and Maximum age of performers - however even that needs to be treated with caution., as the age-groups are based on our guesses - how do we know what your actors are capable of? We have seen some very competent child actors, just as we've seen some hopeless adults!