Yeah, the kid turns into the evil wizard's protege - his good guy dad sees him years later with the evil wizard and he's clearly been turned bad (he has fangs and he hisses at his father, that is. He doesn't push anybody into traffic or anything). So I guess it's the fact that he is now going to be an evildoer. Which, if you look at it from a really broad perspective... surrendering a kid is kind of making it worse for everybody, if the wizard goes around doing bad things.