I ride with my almost 11 year old, and I guess I am fortunate that he will talk to me and listen. I ride beside him when approaching a hill, and ask him how he plans to tackle it. He'll tell me what he is planning. I tell him what I am planning. Then we ride up the hill. If he stops midway, I ride back to him, and he usually tells me if he liked what he picked or not.

I have preached to him that it is okay to shift the back in a hill, but never the front, so he has to make his choice before the hill starts. So far so good. And he still likes tackling hills so I haven't scared him off yet.

And +1 on cadence sensor. It gives an item to focus on. And everyone likes gear.