"The boys on the island vary, of course, in numbers, according as they get killed and so on; and when they seem to be growing up, which is against the rules, Peter thins them out..."

This is a slightly larger quote and I can't say whether Peter does kill them but I thought that quote as a whole made it seem more of a possible idea. (Also he is quite violent and just for the fun of it too- killing pirates and wreaking havoc in the midst of battles are a couple of examples)
I just wanted to say I wouldn't expel the idea, it's certainly an interesting thought to contemplate