I wouldn't put that out of your mind yet, seeing as she was drawing on a piece of paper. Maybe she can 'draw' things into existance. Maybe Isaac's illigitimate child we didn't know about UNTIL NOW!?
Though, Heroes always has a way of grounding characters. Even Peter and Sylar, who could be blown way out of preportion, are still grounded and human-like. This is a character based drama with some very interesting twists, but still a character based drama. It's like what X-Men 3 should've been.
Didn't Matt have a kid? I think someone mentioned (I did miss 2 episodes here and there) that he did. Maybe they bring her back from the future? I know, far fetched.
And ya, why not just go back and kill Sylar as a child or baby or before he found his powers? Only thing I can think of is how would you explain it in that time period, kidnap him and just write him off as missing and never found? I find that there's a lot of "but that would be the easy way!" in the show, but I guess they have their reason for letting things play out the way they do.
And kind of off topic but there was a Charmed (don't laugh, I love that show >.>) where there was a boy that could draw things into existence.