My 3.5 year old transfers from the car at bedtime and has slept through a variety of loud noises in his life. But this weekend we had to room share with the baby and the baby was up all night and kept waking the 3 year old. My mother in law kept going on and on about how odd it was that the older child couldn't sleep through the crying. She even asked if I had talked to my pediatrician about it. Um, why would I do that?

Is it abnormal for a child to not be a heavy sleeper?