Back...slowly...away. Then run.
Nah, it's great having kids but I am so happy I had mine in my very early 30s. Before that, I was probably too irresponsible and selfish with my time to have kids. Now I'm in my mid-40s and I cannot imagine having to expend the kind of energy raising children takes at my age and in the shape I'm in.
My best friend in Texas is a couple years older than me and he and his wife had their first (and only) child when he was 43 or so. He's done a great job of handling it, but I think it's taken its toll to a degree as well.
I am jazzed that my daughters are 15 and 16 now. They are (mostly) independent, interesting, funny, bright, intelligent, beautiful. But I just can't imagine dealing with infants or toddlers where I am in my life now...
A couple years back my wife mentioned something about becoming foster parents or adopting. I just shot her a look that ensures it is a subject that will never come up again.
With regards to kids, I have done my bit for king & country...