The fire test you did was a good idea, we all found out that all material will burn. The reason they suggest 100% cotton for childrens quilts is that unlike polyester, the fabric won't melt and stick to the skin. Polyester will stick to whatever surface it is melting on where as cotton turns to ash. The fire retardant fabrics are good, except after several washings the protection is gone.
Good Luck
Suzy