I have a 2 1/2 year old son and he is 38" tall and weighs 35 pounds. He has totally outgrown his Britax roundabout so today we bought him the Jupitar Komfort Kruiser. We were told at the store that as long as he weighs at least 33lbs. and is not wiggly in his carseat then this booster would be fine for him to use. Since he is not 40lbs. yet, should he not be in this seat even though it fits him well???