DD2 was born 3 days before DD1 turned 15 months, and 2 months after DS turned 3. I'd never planned to have a third so early, so when I got pregnant when DD1 was 6 months I was pretty terrified. It's been absolutely fine - she's pretty easygoing and has slotted right into our family life. It's a bit rubbish going back to night wakings so soon after finishing them with previous baby, but other than that 2-3 hasn't been anywhere near as challenging as I thought it would be (yet!) I'm a bit wary with taking them all out on my own still, but that's partly to do with not trusting a high spirited 3 year old to not run off! I think one of the main things I was apprehensive about was tipping the gender balance - having one of each and then a third leaving one in the minority. Will see how that pans out as they get older, if my 2 DD's gang up on their brother!
If I could afford it I'd have a 4th, so it definitely can't be that bad!!