Getting kids on board with nutrition starts at home. Period. If your kids don't see you do it- they won't feel it's important enough to do it themselves. Tru dat! Where kids lack intelligence, they make up in spades in intuition. They will intuitively follow you: their parent or thier guardian. This goes for exercise too!
Make it a DAILY habit that they see you eat healthy and exercise daily and they will too...it takes a long time to create that habit for you and for them. Now, go! create life-lasting change for the better for all of yours!