I saw this on my wanderings through Pinterest.
I wish I had thought to document the entire process but this will have to suffice. I dragged out some foam rubber scraps and cut them into strips about 18" long. I made one 4 inches wide and the other 2 inches wide and stacked them to create a sort of mound. I wrapped the "mound" with some quilt batting to smooth it out. I did not use the fuzzy backing shown in the picture above.
I made a tube of the fabric with a flap attached to the side seam. Leave the ends open. The hard part is getting that inner stuff into the outer cover. To facilitate this, put the stuffing into a plastic grocery bag and shove and pull it through. The plastic will help it glide. Fold over the ends and sew across.
This flap now folds around the back of the seat belt and attaches easily. All of the padding is away from the child's body so that is serves as a cozy pillow but doesn't interfere with the fit of the belt.
The road test proved successful. He likes it and it went home in Dad's car. Note the bear's trousers. These were made when Teddy got left behind at Grandma's house and he requested that I make an outfit. I made sleep shorts for both child and bear that match although child did not get the neck bow.
I find all sorts of great things to make for girls but not so many for boys and at 6 1/2 he is becoming more conscious of appearing "girly". Although I think those florescent pants might lean that way or are they just gaudy?