Backpack recommendation for tiny kids?

My 5 year old starts school in August. He's a little bitty guy (3 ft 2 and 35 lbs) so I'm worried about him being swallowed by his backpack when he starts kindergarten. Most of the backpacks in local stores are a bit big for him, especially if he is also going to be carrying a lunchkit. And most of the straps are far too wide for his tiny shoulders. Anyone else with a tiny kid? Which backpack have you found that they can carry and walk with easily?