What about friends? do any of your friends have kids, or would make good parents? Basically you have to think next best case scenario so if you can't bring up your kids, who is the next best person? Remember these people need to bring up your child, probably your most precious possession, so you want to be able to trust them and know they are going to do everything they can to make your child happy. We've decided on definitely my brother, maybe my hubby's elder brother or maybe our best friends. We haven't done it yet but are planning to put this in our will, with a clause that both families should make any difficult decisions together, and that if our son lives with one side of the family, a certain amount of time should be spent with the other.
We have also sorted out life assurance, so if something happens to both of us, there is a trust fund to provide enough money until he's 18 to care for him, and also for a small pot for after he's 18 to go to uni, or buy a car or whatever!