Have your child smoosh together the first 5 ingredients in a bowl till blended. Chill 10 minutes. Turn onto waxed paper and using paper as a aid, roll the butter into logsize of nickel. Wrap tightly in new piece and refrigerate 1 hour or longer.
Scrub the potatoes and prick the skin all over with a fork. Bake on oven rack 45-60 minutes, until they're soft and easily piecred through the center with a paring knife.
Serve each potato with 2 coin size slices of butter.