My daughter turned 3 a couple of months ago and is still in her convertable carseat. We are debating whether to invest a high back booster with 5 point harness or just to keep her in her convertable for a few more months and then more her to a booster with seat belt. How long do kids actually fit in a 5 pt harness booster? When is it normal to move to a seat belt booster? I know what the manufacturer says, but didn't know what is "normal" or what other people do.