But the playpen will contain objects that are inherently breakable. You cannot rough handle the glass vessel and have it too.

Basically everything applicable to the playpen of a human baby is applicable to the playpen of an AI robot baby in this setup, to at least some degree.

Perhaps the least applicable part is that "robot hurting itself" has the liability of some cost to replace the broken robot part, vs the potentially immeasurable cost of a human infant injuring themselves.

If it's not a good idea to put a "glass vessel" in a human crib (strictly from an "I don't want the glass vessel to be damaged" sense) then it's not a good idea to put that in the robot-infant crib either.

Give them something less expensive to repair, like a stack of blocks instead. :P

The world Is breakable. Any model based on it will need to know this anyway. Am I missing your argument?