My wife still chides me, "Is everything related to mouthbreathing?". She is the director of a preschool program. She sees the best and the worst of children ages 4,5 and 6. Here is a study that relates the nighttime breathing patterns of infants to their daytime behavior.
This study, out of Einstein, where I now lecture to the ortho residents, created quite a media splash and deservedly so. Take a look at it here.
Then take a look at my online comment to see what they are missing in their study here.
Yes, my dear, it all starts with mouthbreathing.