>>5767813>http://www.hellokids.com/c_29704/kids-crafts-and-activities/how-to-make-clothing-for-your-fashion-doll/no-sew-doll-swimsuitPanties are pretty simple, though I'd personally use 2 pieces instead of one big piece like this pattern uses. Stretch fabric will be easier than adding elastic, though sewing on knits is tricky if you're not used to it. Don't use stretchy material for the strings, though.
The no-sew route looks like ass in the end, so just use this pattern as a starting point.