I was carrying 1yr old boy.i bent down w him to pick up x things.i heard a crack.im afraid if it's his backbone.he didn't cry nothing as normal reac?

Don't worry: can't say for sure, but doesn't sound serious. babies are very resilient. It doesn't sound like you were doing anything that would really hurt the infant; first I would expect him to cry if he was, also if kids were injured every time parents did the same, not sure the human race would have survived! Possibly just a crack from a joint (like when u crack a knuckle) - completely harmless.