Laughing so hard

I am im tears with laughter. My stomach hurts. My 4 year old never uses swear words. He also dosnt realise they are bad. I try to keep it this way so he wont do it as a bad temper thing. But lying in bed there and so innocently and in his wee put on american accent he just done south park saying " you killed kenny, you bastard" its the innocense to it that kills me lmao no idea where hes even heard it from neither