I am aware that my posture is lacking because I see other moms at the play area or swimming lessons or parks, and lots of moms hunched and curved down all the time to get on the same level at the kids. And it has to be comforting for the wee ones when Mom's whole torso curves around them when they're sad or hurt. But, gosh, watching the other moms do what I do all day has made me aware of my hunched back and curvy shoulders.
Without any formal diagnosis or rules, I've just tried straightening up. To keep my back straighter, even when I'm on the floor with the kids. To keep my shoulders back and down more. To keep my chin level instead of either looking down or up all the time.
I found this article about basic good posture. And this one about running posture.