I was contacted by a mother that has often read my blog. She has read it, but apparently didn't follow all the advice. Her 3 year old son was 40 pounds, and riding in a highback booster. He certainly met all the stated minimums for the seat. Except for age. Age can play a crutial role in booster readiness. Her son was riding with her older (college age) son. He unbuckled himself, and no one knew. The little boy fell asleep, and fell out of his booster! He fell out and right onto the floor of the van. In the fall, he hit his face and got a black eye. Mom is horrified. What if there had been a crash? He wouldn't have fallen on the floor, he would have flown out the window! No 3 year old is really mature enough to be in a booster. At my advice, Mom went out and bought a Graco Nautilus. He is now safe and secure in the van. Children under 4 years (often under 6) need to be in a seat with a harness.