There is a ring on the bearing that holds it in place, you can see it on the tire under the trashed bearing, so maybe the sleeve isn't as important.
It's finally warming up enough to ride, we are having a blast with them. The Honda clone engine in my son's kart is great, here is a link to a video with his in the snow.
http://www.youtube.com/watch?v=-HQzbznB1yo Thanks for all of your help!