I've been thinking about this too. After a nearly six year gap between DD1 and DD2, there'll be exactly two years to the bonus sibling. But DD1 loves playing with DD2 already, even though she's only 18 mths and is excited about another sister or brother. I think because DD1 is so easy going and busy with bigger kid stuff it won't bother her as much if the younger two are close.

But, that will depend on personality.

Dreading the younger two fighting already... I'm buying ear plugs!