Ya know, there exists a group called something like Society for Protection of Children that advocates a minimum age gap (I think it's 3 years), for the benefit of the child. I kinda know where they're coming from. I wanted a big age gap, in the end, because I came to learn about child development and all the developing children do in that time is so intense and more changes occur than occur in any other similar period of time in the life span. It is considered fair to be as present as possible for that stage, and once the child reaches about 3 then you have a bit more headspace for the next child, with the first child, theoretically, being more self-sustaining to allow the next child similar headspace.
I tend to concur, because even with a very active 4.5 yo, he DOES understand that his little sister needs me more than he does, even if he doesn't like that fact. I DO talk to him about how much of me he had as a baby and he gets that she needs me, too.
Before being pg the first time I thought I wanted about 6 kids. I'm 35 and two children are killing me! After DS was born I heavily revised my thinking and decided that age gap was more important than quantity. For my own sanity as well as their emotional wellbeing. So this society's thinking really resonated when I heard about it.
DP wanted me to be pg a lot sooner than I was, and really, it was a moot point because I didn't even ovulate till DS was 2.5yo! When I fell pg, I freaked out a bit because I was jealous for my relationship with DS.
And now? I love them both to bits and pieces