Local costume shops and online stores are featuring plenty of furry monkey attire -- which is your easiest option for getting this look. With a little effort, though, you can fashion a do-it-yourself version.
Start with a brown hooded sweat suit or pajamas with feet. Use tan-colored felt to make accents such as a circle on the tummy. Cut ears out of brown material (accent with tan felt circles) and attach them to the hood of the sweat shirt (or to a hat if your child's outfit doesn't have a hood). Fuzzy slippers and mittens make great paws. Finally, don't forget to remind your little simian: No more monkeys jumping on the bed!