After your glue is painted on in designs of your choice, allow the glue to completely dry- then flip the pillowcase over and paint the other side with continuing designs. Allow to dry again. While the second side is drying, prepare your acrylic paints. I wanted pastel colors but only had bold so I blended colors together to make not so bright selections. Be sure to water your paints down. I added equal amounts of paint and water for ours. You want to achieve a sort of watercolor effect with the acrylics.
When your child has painted the first side of the pillowcase, let it dry again and then flip it to paint the second side (be sure to get the edges for them if they're really young) and for a final time, let it hang to dry. After it's dry it will be sort of stiff and probably look like someone let a toddler at a pillowcase with acrylic paints. If it doesn't, maybe your child is a more accomplished artist than mine.
Either way, you now want to pop it in the washing machine on a small load and warm water. This will remove a lot of the paint and all of the glue. Then you're going to dry normally and stop to admire your work so far. Yes, even my art contribution looks like a toddler went at a pillowcase with acrylic paints, but it was fun.
T added lots of dots. and more dots. She's very good at squeezing glue into dots- color me proud.
Next step? Measure your toddler from waist-knee and add an inch to that. Cut your pillowcase to that length, make a very simple seam along the top, thread with elastic and voila!
For gender neutral clothing, this would be simple to turn into shorts, too. If you want to know how to make shorts/ capris and don't know how, let me know and I will very happily talk you through it.