Start them young and make it fun
Is that the actual measured top of seatpost to center of BB size? or is it the manufacturer's stated size?The reason I'm asking is that I have a bike that is right in the 56-57 cm range, and due to the compact frame geometry the top of the seat tube to BB distance is only 54 CM, but there is 3" more seat post showing than on my more traditional bikes. In reality it is a 56-57 cm sized frame.