I made S some pajama pants using some Star Wars fleece I found in the remnant bin at JoAnn. Usually I use CKC's Taylor Pajamas, but I decided to try the Patterns For Pirates pattern called Walk The Plank. The CKC pattern uses a casing for the elastic and the P4P pattern has the main fabric serged to the elastic at the edge, then turned over and topstitched while stretched.
I tried a similar method on the cat pajama shorts and my sewing machine threw a fit trying to sew the stretched elastic (ended up doing a casing instead), but I decided to give it a try with the serger. I previously preferred casings because I could have S try on the pants at the last stage of construction, and also possibly let out the elastic at a later date if I left extra. He usually outgrows by height before waist size, though, and he was around for me to try the elastic around his waist before doing that step of these pajamas.