Jasono,
We used a snow ski helmet when my son was 2 and 3, worked well on trips around home or on the ATV up North and with a mask he stayed plenty warm in the winter. The nice thing is they are so light it isn't hard on their neck. We went to the more traditional helmet when he started riding the snowmobile trails with me, I felt the need for more protection given I was now worried about the other people out there.
Enjoy