Noting your edit that this is about actual children, not adult children: Only secondarily. Lots of people can be friends in life, but you only get a small number of parents/parent-figures, and they're needed. You should be friendly enough with them that you can become friends in adulthood and you can be friends when there aren't any active issues under management, but you shouldn't be so attached to being their friend that you won't be hard when you need to be. And you need to be able to withstand the periods when their development requires them to go against you. They do need to rebel a little in order to become independent adults, they need to be at least willing to reject you and what you stand for, at least for a little while. That shit hurts anyway, but it will hurt a lot more if you're overly attached to the idea of them as your friend.