If I felt there was a danger in having children post WLS I wouldn't have had it. I had the surgery for several reason, including my infertility due to being morbidly obese. I was told if I lost 100 lbs I would be able to have children.. so we'll see..
There are a few people I know of who have had or are having children after WLS. The safest thing to do is to wait about a year before getting pregnant. By then you can eat PLENTY of food for a fetus to survive. Of course you still don't want to get into that habit of thinking you have to eat for 2.

I don't know any baby that eats as much as an adult anway.. lol
It is much safer to carry a child after WLS and at a healthy weight than it is being morbidly obese.. and from what I hear.. much easier on the Mom too.