he can’t grow up ????
So he resorts to killing it??
A vampire ages physically slower than humans, that’s why a 160 year old looks like a 16 year old..so he might just be growing like a vampire
And even if he isn’t growing, you can still raise him with your pookie, nothing stopping him ╮(￣▽￣)╭
Or in this case, taking care of the baby, not raising it
nacht said he has been looking after the kid for hundreds of years so, in this manga's logic, they do not age at all
Why kill the baby, raise him with your pookie, duh