Can a child on a subclass 102 visa travel in and out of Australia?

A subclass 102 is a permanent visa, so the child can travel in and out of Australia during the travel facility period attached to the visa, which is usually a set number of years from grant.

If the travel facility expires while the child is overseas, or if they need to travel after it ends, they would generally need a Resident Return visa to re-enter as a permanent resident. The right to live in Australia as a permanent resident does not expire, but the ability to travel and return does need to be kept current.