I would think that a kids ski helmet would be best. They are desined for the cold, so it will make them more comfortable. Some of them are adjustable, so as the kid's head grows, you dont need to buy a new helmet as soon. They are very light, and can accept goggles.
I would recomend a Giro Richochet, as it is adjustable.
http://www.amazon.com/Giro-Ricochet-Snow-Helmet/dp/B000JLB6XK
I would recomend a Giro Richochet, as it is adjustable.
http://www.amazon.com/Giro-Ricochet-Snow-Helmet/dp/B000JLB6XK