Question Regarding Child Overheating

WOW how interesting! Alex almost 2.5 years has been home for 2 years. He is VERY fair skinned, but turns red almost as soon as he gets outside. He also gets a really sweaty head, mostly in the car even with the air going full blast. He came home at amost 6 months..could that have been long enough to develop rickets? Jackon was adopted at the same time and was 18 months and does not have the same problem. He has olive skin and gets brown as a berry during the summer.