they are very very cute - and affordable!
Here's what you'll need:
A pair of inexpensive cotton leggings*
1 kitchen sponge (or a proper stencil kit if you have one)
*Leggings for boys are hard to find so always browse the girls' section
for gender-neutral colours. We found navy, black and striped ones there!
Using scissors, cut your sponge into the shape you want to stamp onto the leggings.
Dip it into your fabric paint and dab off any excess onto a paper towel.
You may want to test out your stamp onto a piece of paper first.
In my case, I ended up going over every triangle a second time so that the white popped more. I like that the shapes were't perfect and a little washed out.
Once the paint is dry, go over it with an iron for about 5 minutes to set
(or follow the instructions on the label).