MiniMonster has the most awesomely adorable onesies, t-shirts, and bibs you can imagine for your little monster. The lovely Connie there was fantastic with me regarding a custom order I wanted done for my Demon Child. She lists up to 4T, but went beyond the extra mile for me and made up a 5T for my boy in this.
Check out her shop...you won't be disappointed. Her prices are great and the best part...she has free shipping through the end of September!