I did these baby vests cross stitch last year before my daughter was born. It is very easy and takes a little time. I used the aida left from the previous project. Firstly I attached the aida on the vest by stitching the edge. After finishing the ladybirds and the pink little pig, I took out the aida line by line. The normal vests turned to be designer clothes right away.
The only problem is that the back stitches might a bit rough for the baby's tender skin. But my daughter did not seem to be bothered.