I think what children were doing in medieval castles usually depended on the social status of their parents living in those castles. So a child of a cook was supposed not to play with that of the owner of the castle. But depending of their age; the younger a child is, the more ignorend he is about status of his playmate.
Medieval castles.
There is nothing different between todays castles and medieval time castles. Today's castles were built in medieval times.
The welsh medieval castles were big and gray.
Medieval times
in the late medieval period many medieval castles did have a primitive type of cannon.
Castles were invented in medieval times.
There are no genuine medieval castles in the USA, because the Americas were not discovered until after the medieval period had ended. There are the "fairytale" Disney castles and some modern attempts at reconstructing medieval castles, but no genuine ones.
Motte and bailey castles, Stone keep castles and Concentric castles
Who is most important in medieval history - kings and emperors. Where do they live - in castles.
Life
medieval Europe
Medieval castles evolved because the old Motte and Bailey castles where easier to set alight and where not very strong, so they made stone castles to improve defence.