Be mindful that the middle child has the skill and talent to be helpful, so there doesn't have to be a routine of having only the older child in charge.

I don't think it's a terminal position and it's not that damaging. If you find yourself having a third child, the best thing you can do for any child is treat them with respect and as the individual that they are.

My guess is that they are probably good parents, too, because of their own sensitivity to that position of being a middle child.