My 3.5 year old asked me this today. I said that all people are different shapes and sizes and it's just the way they are, but we shouldn't really ask because it might hurt their feelings. (I was a bit aghast and slightly upset as she's asked less directly before and I've batted it away by distraction!)
In hindsight, I think it was a bit of a defensive answer. The real answer is a combination of the following: I had her little sister by c section last New Year's Eve; 5 weeks later I had a hysterectomy via a vertical incision to remove a fibroid which had taken over my uterus because it weighed 3.2kg/7lb, almost as much as her little sister did; I like chocolate and other nice but naughty food; I like exercise if I don't realise I'm getting out of puff because I'm into it, rather than exercise for its own sake, and I've not had much chance to get into any this year! I also have mild PND (again) and will be going to my 1st CBT session in the new year.
I don't like my body now I have a front bum because of the vertical scar. It puts me off doing anything as I don't feel it will go whatever I do. I never diet, I just increase my exercise, and I don't eat awfully too much of the time. I'm a 20/22. Having said that, I'm still confident enough to be naked sometimes at home, and I want my little people to know it's what people are like on the inside that is the most important thing of all.
So the question is really, what do I say if she asks me again which is perhaps a little less defensive and more positively educative?