"I can't believe you have 4 kids"

I have returned to the work place.  In body of course, not exactly in mind. What I find interesting is that everyone kind of left me alone for the first month or so. They think I'm going to be overwhelmed with emails etc. so they just pop in to say hello and leave. I have a feeling in August I will get 4000 emails.
The one statement I hear on a regular basis is  "you don't look like you have had 4 kids" or "I can't believe you have 4 kids"
What does a typical woman who has 4 kids look like anyway?
My response to this is usually a smile. I honestly don't know if its a compliment or not. Like, based on my maturity level, I cannot handle 4 kids. I'm possibly reading too much into it. But if you think about it how a women is expected look is kind of determined by their region.  Say I'm in LA where women are expected to look like a model 3 months after they deliver but I live in the midwest. Where its perfectly acceptable to have a belly 5 years after you have a baby.  I however believe that a combination of diet, a lifetime of exercise, and genetics, have made it possible to lose the weight quickly.  With that said, I in no way am 100% delighted with the way my body looks.
No way, but have I ever really been?