Sesame Street Characters Alphabet T-Shirt or Elmo Initial Alphabet T-Shirt. Each are $14.99 at Identity Direct and you can personalize with your child's name - up to nine characters on the first and 11 on the Elmo.
Or you could consider the big face shirts that have been the rage lately. Walmart carries them for Elmo, Oscar, Abby Cadabby, Cookie Monster and Big Bird.
The other line I've found are the Elmo Loves ... and Abby Loves ... designs over at Personal Creations. You can get the design saying the character loves your child on t-shirts, rompers, even hoodies!
Disclosure of Material Connection: Some of the links in the post above are affiliate links. This means if you click on the link and purchase the item, I will receive an affiliate commission, probably enough to get a stick of gum. I generally only recommend products or services on this blog that I would use personally and believe you will find cool as well. I am disclosing this in accordance with the Federal Trade Commission’s 16 CFR, Part 255: “Guides Concerning the Use of Endorsements and Testimonials in Advertising.”