A.B.
My children are almost 4 & 2 and 2 months...they all share a room right now and all have different bedtimes. My oldest knows not to wake up her sister when she goes to bed. I think that as long as your 3 1/2 year old knows the rules and the consequences for breaking them, you should be fine...I'd give your 10 month old at least 1/2 hour before putting your 3 1/2 year old to bed.