I'm not sure that it's sick as long as you know that you wouldn't do anything to make them disabled. The only two ways I know of to have disabled children are 1) to have a disability yourself that can be inherited and 2) to have children after 40 (if you're the woman). Maybe to eat/drink unhealthy stuff too. But again, I think it would be wrong to try to make them disabled.

I hope you leave the option open to adopt disabled children, if you know that you are capable of caring for them.