I just wanted to show how I made a sweater into a really cozy and convenient car seat cover for Baby B (in the picture it's a dolly).
I used a men's sweater that was a nice thick really soft wool, with a zipper up the front. It actually has a double pull so you can zip up from the lower edge if you want but that is not necessary for the cover, although it is handy. I washed the sweater and was intending for it to felt, it didn't shrink very much at all, this turned out good since the zipper needs to lay flat. I checked to see if it had felted at all and it seemed satisfactory for the purpose here.
I cut the sleeves off and cut up the side seams, placed the sweater (zipped up) over the car seat with the neck hole where baby B's head would be so that it would work as a face or neck hole for him. Then I folded the lower front edge around the edge of the car seat and pinned it at the sides, this will work best if you have the sweater inside out so that you can just sew where the pins are and turn to get the desired effect. I had a lot of extra sweater at the top edge so trimmed it off leaving a few inches to wrap around the top edge of the car seat to hold it in place. I took a large dart in each corner to follow the contours of the seat and stitched 1/4" elastic on the underside of the edge to stabilize it and keep it from sliding off, as well as along the lower front edge for the same reason. Then I cut 2 strips about 1" wide and long enough to reach to keep the sides from gaping open, stitched them on cut button holes in them (slits really), and stitched salvaged buttons on.
In retrospect I should have put the button at the other end of the little strap so you can See it as the hood covers the button now and no one ever sees it, if I had ugly buttons that would be perfect but I used cute ones so I wish they showed.
Baby B likes the cover when it's cold and windy and it keeps him from loosing his blankets while he's kicking his little feet, also helps contain socks and booties that get lost otherwise. It cost me about a dollar for the sweater on tag color day, and the buttons were salvaged from a jacket my MIL gave me to use for re-working. I love the buttons by the way.
The neck hole is really not as large as baby B's face so usually if he is awake he likes to have his whole head sticking out and wear a hat, rather than have the hole around his face. All in all I really think it worked out, and sure beats draping a blanket over the whole car seat and having the wind blow in there and the blanket sliding off and dragging in the slush and mud.