I've never used the paints, but I did do handprints on a family quilt. I had each member trace their hand on the paper backing of wonder wonder fusible webbing. I had them write their name inside their hand, so I knew whose handprint it was when I went to place it on the quilt.
I then adhered the fusible webbing to fabric and cut out handprints. Each person signed the front of their hand print. I'll post a picture of the quilt so you can get an idea.