Try it on, and go play.

Make a toddler dress from a t-shirt. by domestic_engineer

Step 6: Try it on, and go play.

Make sure all the pins are out. Trim any loose threads, and put it on your kid. They will love it.
Here they are playing Super Hero Girl, and her trusty sidekick Robot Girl.

Both were size Meduim men's shirts. The blue is about a size 6 girls, and the grey is about a 2T/3T.