I want some videos that show him the importance of correct seating in a booster. In my van he's in a high back booster. When he goes with grandma she's got a backless booster for him that he slouches in.
He's on his last chance right now. I told him I'm gonna show him some videos and he's gonna start sitting in the seat properly or he's going back to a 5pt harness
Post links or videos of stuff I can show him tomorrow!