From Patterns for Pirates:
This is a very quick and easy beginner friendly pajama bottom. It is a elastic, pull on pant with no side seams. It has a loose and comfy fit for snuggling in at night. It is drafted for non-stretch woven fabrics like flannel or cottons. The pattern and construction are fast as lightening so you can whip up a wardrobe full for you and your family in no time.
If you are new to sewing there is a video link in the tutorial of the construction.
Options include mens/higher rise, women’s/lower rise, short shorts, knee length and pant length with 30″, 32″, 34″, and 36″ inseam lengths. The plus 3x size includes both no side seam and with side seam option (this is so it will fit on a smaller width fabric that is more available).
Here is a round up blog post and album full of photos to look through!
You can also grab the youth pattern here: Walk the Plank PJ Bottoms- Youth
Sizes included: XXS, XS, S, M, L, XL, XXL, Plus 1X, Plus 2X and Plus 3X.