Follow your heart. If you feel you are raising your kids well, be diligent in your parenting and stay aware of your convictions. You are only responsible for teaching your children behave and respond to others. You aren't responsible for how those other kids behave.
There are several families in my old church who advocate this class and seeing how they are and how their children are, which matches your description of Growing Kids families, is the reason why I never got involved with it. I too, share your observations. You are not alone. The parents come across as major control freaks. They have ZERO tolerance for disobedience in their kids and that expection sometimes seeps onto other kids not their own. The kids seem sad and depressed, as if they are on edge, as if they'll be caught in disobedience at any moment. Neither the parents nor the kids seem to have any life. They are literally lifeless. No joy, no harmony, no happiness. It shows on their faces, which are usually blank, expressionless and void of any joy. Most of these kids hardly have any manners. They aren't friendly kids. If I say hi to them on Sunday morning, they literally just stand there like duds and stare at me....until their parents order them to say hi or good morning. Its as though this class teaches these children to only recognize the existence and authority of only their parents.
I've never taken the class but I've been around enough families to see the harm this class can do when its wayward theories fall into the wrong hands, with wrong hands being defined as control freak parents who want to rule over their kids with authority; lazy parents who don't want to take the time to teach and nurture their kids how to behave in a world where other people, not just their parents, have authority. I know there are alot of Growing Kids moms on this site and I don't see any of them rushing to defend this class. Maybe you have made us all aware of something that needed to be brought to light.
If that little boy throw your daughter's food on the floor again, I say to take his food and throw it on the floor. See how he likes it! (I know, that part isn't in the Bible)