"Tucked In" Toddler Shirt

My little 3 year old gets to go to preschool this year.  She started today, in fact.  One of the most exciting things for me was to go shopping for her school clothes (by myself).  I picked up a couple of t-shirts that would look so cute tucked into the skirts that go with them but it's hard to keep a shirt tucked in with a toddler.  I thought about just tying a knot or using a safety pin in the back but that didn't look right.  I decided to add some elastic to the bottom of the back of the shirt so it just looked like it was tucked and I never have to worry about fixing it.

I sewed the end of the elastic at the bottom hem, starting at the side hem.  Make sense?

Then I pulled it tight and sewed all the way to the other side.

Here's the other one that I did.