Mine were nearly 6 and 3 when DD2 arrived. I just don't think I could not do it with younger kids. There's a reason mine came when they did I think. I had no nappies or prams or night wakes each time another came along. DD1 is the worlds best big sister, but then she was great at nearly 3 when DS arrived too. I don't really have experience any other way, though earlier this year I looked after a NB. DD2 wasn't quite 1. I take my hat off to mum's with babies close together. I personally found it really hard.