Hmm. I would never leave a toddler with a baby, even when they are supposed to be asleep. What if she wakes him up and he wants to "help" put her to sleep? Or if he wakes up and wants to play with her? I can just see the dangers here. I believe SIDS guidelines say baby should share your room for a year and NEVER sleep with a toddler.

Plus, I think the boy may have issues with having to share his dad - he has to share his time between parents but his sister gets Dad all the time, IYSWIM. And if he no longer has "his" room but has to share with his sister when he's not there... I suppose I am creating a problem that may not exist, but it's worth considering.