I'm not sure which adjective fits best, but this may be the most annoying, stupid, or rude question to ask a couple:
Why don't you have kids yet?
It doesn't seem like there will often be an answer that won't hurt some feelings, after all, either the couple:
- has decided not to have kids and are true DINKS (Double Income No Kids)
- does want to have kids, but are having problems with infertility
- is not ready (maybe one or both of them) to have kids yet
If you are close to the couple, then you will likely already know their plans for the future and whether or not they want it to include kids. Otherwise, maybe wait until they let you in on their plans, If you must know, then consider asking in an indirect way, such as by asking 'have you thought about having kids someday?'