The funniest thing here is the prep (I had to do it) took longer than most things! I cut out the letters of Gabriel's name from painter's tape. This is an 8X11 & 1/2" piece of paper. I'd suggest using a bigger poster-size sheet & just creating large, block letters with the tape!
All you have to do is, using painter's tape, apply child's name. Allow the child to paint over it... Then allow the paint to fully dry. Carefully peel off the painter's tape.