A disappointing message.
I can see your point of view of how the man doesn't want the kid to grow up like him and all, but I find that point of view to create an air of naivety and disgust for the main character. After thinking for, say, not very long at all, I think you should at least have a gut feeling that something is amiss -- the child abuse and the murder. The audience should feel that the main character should report the abuse to a nearby police officer (don't parks usually have some type of police?) and even if he does murder the guy he should not do what he did afterwards. Disregarding the aforementioned, if he didn't want the kid to grow up like he did then why doesn't he just put him in an environment where he isn't beaten with a shovel? Hell, put him up for adoption at least? That is if he isn't prosecuted for the brutal slaying and the kid isn't put in someone else's care anyway.
Then again, that might have been exactly what you were aiming for, to despise the main character's terrible choice and think of him as a naive lunatic. Stuffing the kid in a toilet would definitely be most heinous. Perhaps an allusion to the terrible choices we make in life without thinking things through that hurt other people? Perhaps the metaphorical baby killing rampages we go on were what you were really getting at?