Sarah says "2 1/2 year-old" and "decorating cookies" in the same sentence. She MUST have a hack.
OK, so my cookie hack is to make a simple, runny icing from powdered sugar, milk and vanilla. Make a ton. Then separate into bowls and add food coloring until you have as many colors as you want.
But the "hack" part is to give your kid an ice cube tray with a little icing in the different sections then a bunch of baby spoons to spread or drip it with. The photo is of my (then) 2 1/2 year old decorating Easter cookies. He had a blast with it. I just gave him 3 or so at a time to "paint" on a cookie sheet and it worked great. Minimal mess, tons of fun.
Is that a picture for the scrapbook or what?