Does Islam allow child slavery? From which age? What are the restrictions?
Islam accepts/accepted slavery because at the time Islam was revealed, slavery was deeply rooted in the community that it couldn't be cleared at once. However, Islam doesn't allow enslaving free peaceful people for any reason, be them Muslim or non-Muslims.
So if someone is free (i.e, not a slave to anyone else) and peaceful, then Islam doesn't allow anyone else to enslave him for any reason.
And that's a general case, there are no specifications regarding age, gender, race, color... etc.