I also put on about 18kilos per pregnancy but a lot of this was water retention (I retain very easily). I peed soooo much after the births and lost the extra weight fast without really dieting. Breastfeeding (for me) simply sloughs off the extra weight. I'm usually lighter after 9 months of breastfeeding than I was at conception. Carrying a baby in a sling also helps I think (to lose weight).