any sugar glaze with enough sugar to harden and not stay a sticky mess will be "too sweet"...the clue is to make a frosting heavy enough to stay on top of the cookie and not sink in...That would be royal icing.
Of you can just sprinkle the cookies with colored sugar crystals. That's what I do most of the time.
Linda C

This is a little late for your Halloween cookies, but for the future here ya go:

For Royal Icing with Egg Whites: In the bowl of your electric mixer (or with a hand mixer), beat the egg whites with the lemon juice. Add the sifted powdered sugar and beat on low speed until combined and smooth. The icing needs to be used immediately or transferred to an airtight container as royal icing hardens when exposed to air. Cover with plastic wrap when not in use.

For Royal Icing with Meringue Powder: In the bowl of your electric mixer (or with a hand mixer), beat the confectioners' sugar and meringue powder until combined. Add the water and beat on medium to high speed until very glossy and stiff peaks form (5 to 7 minutes). If necessary, to get the right consistency, add more powdered sugar or water. To cover or 'flood' the entire surface of the cookie with icing, the proper consistency is when you lift the beater, the ribbon of icing that falls back into the bowl remains on the surface of the icing for a few seconds before disappearing.

The icing needs to be used immediately or transferred to an airtight container as royal icing hardens when exposed to air. Cover with plastic wrap when not in use.

Makes about 3 cups

Royal Icing Using Egg Whites:

2 large egg whites

2 teaspoons fresh lemon juice

3 cups (330 grams) confectioners (powdered or icing) sugar, sifted

Royal Icing Using Meringue Powder:

4 cups (440 grams) confectioners' (powdered or icing) sugar

3 tablespoons (30 grams) meringue powder

1/2 teaspoon extract (vanilla, lemon, almond)

1/2 - 3/4 cup (120 - 180 ml) warm water

Royal icing gets really hard!! Remember Lucy Johnson getting married in White House & they couldn't eat the icing-rather embarassing!A simple as you get icing is 2 C powdered sugar sifted, 1 tsp butter melted, few grains of salt (take little between your fingers-reason is it cuts the p. sugar taste like 1/16 tsp or less) then little of 1 of following, cherry juice from bottle of good flavored maraschino cherries (pink icing)so you can spread it or 1 tsp vanilla,almond, orange extract & either water or milk until thick enough to spread. Should not run all over. Just frost 1 or 2 cookies & then put sprinkles on, can't frost the whole batch &then do sprinkles as it set up fast & sprinkles will roll off. Try for xmas cookies, have kids do decorating with sprinkles while you ice them. Good luck!!For colored icing add about 1/2 drop coloring, way you do that is drop on spoon & then blot some off onto paper towel & throw out. I like pastel cookies not real dark colored.Freeze cookies in flat covered container between waxpaper for several months. I start baking & candy making tomorrow for xmas.

Hopefully these are the ones you are looking for. I grew up with these recipes and they work every time. Enjoy!

Sugar Cookie Glaze
1 cup confectioners sugar, 1 tbsp light corn syrup, 2 tbsp water, food color
- dries quickly, must stir each time otherwise it gets lumpy

Sugar Cookie Icing
1 cup confectioners sugar, 2 tsp light corn syrup, 2 tsp milk, 1/4 tsp vanilla/almond extract, food color
- use to paint or dip cookies

The fastest, easiest way to get sprinkles, colored sugar, jimmies, etc to stick to a cookie is to brush it with a light coat of corn syrup or Wilton piping gel. The good thing is neither dries so quickly that children have any trouble getting the decorations on before it dries--there's no rush. You do need to let the decorated cookies dry until the syrup or gel is completely dry. When dry, the cookies will be nice and biteable! Not hard as rocks as can happen with Royal Icing.

This makes for a REALLY fun and relaxed cookie decorating experience for everyone. I give each child a cooling rack of brushed cookies with paper plates or waxed paper underneath to catch the inevitable spillage of decorating materials so the excess can be reused.

Have a blast with the kids and make sweet memories without a ton or work or horrible mess to clean up!