DD is just 2 and has been in the Britax Duo Plus for a couple of years. Weight-wise she's 15kg so within the max 18kg weight recommended for this car seat, and right at the bottom of the next seat up. She still falls asleep in in the car so I like how much support this seat gives her. BUT, her head is now right at the top of the seat - is there any height recommendation for seats or is it just weight? Britax website just seems to mention weight.