This is the elizabeth zimmerman pattern for knit longies, done up as pants. They were a very easy and straightforward knit. They are super stretchy and seem like they'll be comfy for baby. I did them up with the elann.com esprit, which is almost all cotton with a touch of elastic. Should be comfy and somewhat easy care.
The elastic kind of crinkles up the cotton, so the knit fabric has a really nice texture. I also knit it at a pretty firm gauge, the yarn recommends a size 7, but I used a 4. Hopefully that will also add to the durability.
I bought a ton of this on a "full bag" sale, so I had 10 balls of each color. Plenty for a ton more baby pants, but I think I'll be waiting for something else to call to me as the perfect project.
Knitting tip: When I switched from the purple too the ribbing at the bottom edge, I did the first row of green in plain knit which gives a plain clean line on the transition instead of the color breaking you get on the purl side of the fabric when you do stripes. It makes the top and bottom ribbing both look equally clean and tidy.