One thing I would consider is what would happen if your DGS chews on the painted parts of the quilt? You don't mention if he is still a baby or toddler or what. Having it on clothes is one thing but on a quilt, it is too easy to put their mouth if he is still a baby. I don't know enough about it to know if it is non toxic. Why not just do fusible applique letters and blanket stitch or satin stitch around them?