Use foil wrap around cookie cutter, leaving top open. If the cookie cutter could go in the oven you could let your children melt crayons in it and have one big crayon with many colors. Place cookie cutter on a cookie sheet lined in tin foil and put broken crayons inside a cookie cutter.
Put in 350 degree oven and continue to watch until all the crayons have melted into one. Use assorted colors but do NOT mix once the wax starts to melt or you’ll get an ugly color. Remove from oven and let cool.