Before I got pregnant the first time, I was one of those people who was *freezing* all the time. I had a friend who used to laugh his butt off at me-- I would be wearing a parka, heavy jeans, boots, gloves and a scarf and he'd be wearing shorts and (maybe) a sweatshirt. He said that the problem was Brown fat, and this is what I've learned:
When a child is forced to wear a coat when they don't need one, or a child is raised in a consistantly warm environment, they lose the layer of fat that's designed to keep them warm. You can't ever grow more of this fat-- once it's gone, the only way to deal with cold weather is to either a) build up a tolerance or b) pack on the layers. :LOL In other words, every time my mother made me put on a jacket when I wasn't actually cold enough to need one, that fat layer was breaking down more and more until I eventually needed a jacket in weather that was even vaguely chilly. As a result, I required a seriously expensive jacket just to be able to function out of doors (and do things like walk from classes to the bus stop) at all when the temperature dropped below 40 degrees. I will never ever force my children to wear jackets because I'm cold; I just keep a jacket or sweatshirt in the car for each of them, just as I keep a sweater for myself all year round, in case it gets chilly.
My kids have very different ways of dealing with heat. BooBah is completely incapable of functioning if she gets too hot. She refuses to sleep under blankets *at all* unless she's sick or the temperature in the room is around 55 (at which point she may or may not concede to a sheet). When the ILs air conditioning went out, BooBah was unable to sleep at all-- she spent the whole night screaming in frustration and only fell asleep when I put her in the car and turned the AC on for her, poor kid. Even now, at 15 months, I trust her judgement: if she's cold, she'll ask for more clothing and if she's warm, she'll peel layers off (everything but her shoes, she loves her shoes.. :LOL).
BeanBean tends to run warm and doesn't notice cold weather until it gets below 50. He'll often take note of a chill in the air but be perfectly content to wear a jacket or not wear one, based on my suggestion. The big difference between BeanBean and his sister is that he *prefers* to be very warm to being chilled; he'd rather have an extra layer on than not.
BeanBean is perfectly content to put on a blanket sleeper in the middle of August, and he will not under any circumstances sleep without a blanket, even if the only blanket available is unbearably warm and it's very warm in the room. This can be a big problem when he wants to sleep on your lap outdoors in the middle of July, and the only blanket he can find is a giant, heavy quilt sewn by one of his great-grandmothers. :LOL