DD is 4.5, about 17kg and her ears/eyes are about 1.5 inches below the top of the car seat. She is FF. The manufacturer says that the seat will be outgrown at 18kg, or when her ears/eyes are level with the top of the car seat. But when I was putting her in yesterday I noticed that the straps are slightly below her shoulders. A quick google suggests that for FF straps should be at or above her shoulders. I've held off getting a new car seat as everything I read said not to go up to a hard back booster for as long as possible, but do the straps mean we should get her a new seat now?