Upcycled boys boxers

I love the idea of being able to reuse old Tees so although i am a bit afraid of stretch fabrics, I could try this idea because it is costing me nothing.
I came across this at http://www.sewastraightline.com/2011/03/lets-celebrate-with-underwear.html and thought why not give it a go.
And for the cost of a bit of elastic, this is what I came up with.

Not too bad for two (almost) free pairs of cute Big Boy undies for my little boy.

Now i just have to figure out how to make them in bigger sizes??