I've just found out that ExH is using a booster seat (no back/sides or head support) for our 4yr old DD. I have her in a proper car seat and I'm really safety conscious about things like this. He has got 2 other children and so has probably put her in the booster to get all the kids in his car but he drives a massive Volvo 4x4. Not sure how to handle it. I'm assuming it's legal?