They had made something rather similar from sweat pant material and ribbed knit waist band. I found my fabric on a "designer samples" table, so it isn't the standard off-the-bolt quilting cotton. It is ever so slightly heavier (at least it was until I washed it) and slightly sateen finished.
I didn't have ribbed knit for the waistband, but I had a substantial nice quality knit and it worked quite well.
They had hearts on the knees (and theirs didn't show up either), so I decided it might help to keep it from tearing if she falls and scrapes her knee.