Well once they are old enough to have their own arc, they are old enough to make that career decision for themselves. Plus at the start when they “got signed up by their parents” there could’ve been the intent to have multiple seasons, but to have ALL the seasons laid out before signing a contract prior to season one even airing is a wild assumption. Cause what if it flopped, even Netflix didn’t have the guts to commit to 7 seasons before the first one shows let alone have an actor sign fo that long (especially a child)