How do they decide what size to make, car seats, pushchairs, etc? My LO has been off the charts for length and weight for a few month snow and her head was above the top of her stage 0 car seat at nearly 6mths. She is 12 kgs but most pushchairs only take a safe weight of 15kg. Do they make measurements based on the "average" sized baby? Like the red book chart average? Pointless thread but something that has bugged me for more knowledge for a while.