My DD is 20mths and very very rarely sleeps through, like she's done it maybe....6 times in her life (at home, when we sleep at nana's she sleeps through often.....). She's going through a rough patch at the moment and we can be up more times with her than with DS, up to 6times a night! DS wakes probably 3 times for a feed, he's cosleeping and doesn't often get to cry before I shove my BB in his mouth, LOL! So I haven't had the issue of him waking DD (she's in her own room in her cot). DD doesn't usually wake DS, though sometimes he will wake after she's been screaming, or woken at night.