Yes, it snows in Hawaii. And the snow adds to the already-impressive sights at the top of Mauna Kea on Hawaii's Big Island.
It is not hard to drive from sea level to the nearly 14,000' summit of Mauna Kea (with the right 4x4 vehicle and the right conditions) in under 2 hours. It is also not hard to get mountain/altitude sickness by doing so. Even after acclimating at 9,000' for nearly an hour, I could feel the lack of oxygen. Children should be monitored especially closely if attempting this trip.