My son is 5 now. My wife and I started noticing that he had poor posture a couple of years ago, and it seems to have gotten worse. He slouches and rounds his back while sitting, and his shoulders always seem to be rolled forward. I'm really at a loss as to how or if I can encourage good posture. Our pediatrician told us (about a year ago) that he has no bone abnormalities. It seems he's just developed poor habits, probably to some degree influenced by myself.
When I see my son slouching, I will occasionally tell him to imagine that he is being pulled upward from a string in the clouds, because this is how ninjas sit (he idolizes ninjas currently). I prefer this to the "sit up straight with shoulders back" approach, because I think that can also lead to bad posture. However, what I've been trying seems not to have been working. I suspect there may be emotional/psycho-somatic issues at play.
Does anyone have any tips?