It came out that DD will be 5'5". Probably right. She's 12 and 5' now, and DH and I are very near 5'5".
I know they are WAY off on my son. He's 10 1/2, and weighs 55 pounds (always been REALLY skinny) and is about 4'10". It says he's going to be 6' tall. Not in my lifetime! I can guarantee it! Tallest person in DH's family is 5'6", and most of them reach their height by about 14.
Given what other people here are saying, it must be the weight thing throwing it off. Maybe the program assumes that since the child is thin, they haven't hit their growth yet?