So, I became a Godmother yesterday (it was amazing and I have the BEST goddaughter) and I was also allowed to make her baptism outfit. One of the things I made her was a nappy cover, only we weren't sure on the size, so I made a test one to check!
It's printed poly-cotton and I top stitched in white.
It was too big so Goddaughter has it for when she's bigger and we made a slightly smaller one for the big day.
I used this tutorial and this is the 6-12 month size. The only area I changed was to turn the seam allowances in and hem them down.