What Is THE Toy You Would Get If You Could Travel Back In Time?

I have a bit of an issue with Thursday's epsiode of HEROES (Season 3 / Episode 12 / "Our Father"), where Present-Hiro and Present-Claire travels back in time (16 years) - particularly when they stood next to their younger-counterparts (present-Claire with baby-Claire-bear, and Hiro with Kid-Hiro) = Doesn't that affect the space-time-continuum? Shouldn't their existence cancel each other out? Or