Gotta say though, the dynamic when multiples are in the mix is very different. Sometimes harder, but sometimes easier. I had three, 4 and under (two under 2 for a while) and my best friend has children very similar ages to mine (a few months between them all) but she has 2 sets of twins. It's just different. She's already looking at heading back to work, goes to the gym every day etc etc. The age gaps are staggered differently cause she has two at the same age/stage iykwim? Whereas I still have a 2 year old and a baby.:
My twins are almost 2 and are such a joy
Anyhoo...I don't know what I'd say. I have toyed with the idea of having another but honestly, don't think I'm going to push my luck. I feel very lucky to have the three I have and life is busy enough I think. At bed time especially I wonder how I'd spread myself even further if we had one more.
BUT if I were going to have another, I'd probably go for the same age gap I had between my boys. So about 20 months. I found that worked really well. There was a 2.5 year gap between DD and DS1 (not by choice but that's the way it worked out) and I found it hard going back to the nappies and sleepless nights. This time has pretty much been a non event.
Also agree with Mbear about kids going to school - if anything, it just makes for a busier day with the drop off/pick ups etc and you'd have 3 little ones in tow. I found that when DD went to preschool. I guess it might make it easier for me to get out with just the boys, but with nap times etc it'll be a pretty busy day!
