Their children were having a hard time keeping round "bubble hands". Their hands kept drooping below the keys as they would play. Well, this would not do. It's harder to play this way, but injuries could also occur. The correct way of playing is to have rounded fingers, and wrists level with your forearm. So, How do you correct your child's playing position and keep his hands from drooping?
To make sure it wasn't a matter of forgetting or something that just needed more time, I made sure the parents were reminding them to keep a "bubble hand" by saying things that helped them correct it like, "Your bubble popped! Can you fix it?" She was constantly doing that and wanted to know what else she could do. Then I realized the problem was probably caused by them sitting too low at the keyboard. And this brings me to the point of the post.
These little chillins are short! Piano's are for big adults. Your child really should be boosted up on the piano bench 3-5 inches so that their relaxed, ready-to-play forearm, is above the keyboard. Make sense? Their wrists won't fall below the keyboard anymore if they're raised up. I can imagine their "bubbles" would flatten a lot with the weight of their arms working against them. So, a stack of books under the bum should do the trick. While you're at it, place a stack of books or a footstool under their feet too, as their weight should be slightly on their feet.
This video should make it clearer for you :) This is for an adult, but it can still give you an idea.