I find Royal icing made with meringue powder much easier to work with but my kids and I don't like eating it. Windows can be made easier by putting crushed candy in window openings and melting in the oven.
Gingerbread House Glue and Windows

Icing Glue

Beat till slightly foamy:
2 egg whites

Boil:
2 cups sugar
1 cup water

Boil syrup to 248ºF. Pour syrup slowly into beating egg whites. Beat until cool. Place in medium freezer bag. It dries quickly if exposed to air.

Windows

Boil until clear:
1 cup sugar
1/8 cup water

Remove from heat and pour onto tinfoil marked with window outlines. It will continue to darken. Makes about 10 medium windows