From Lowland Kids:
The lounge sweats are the easiest and quickest Lowland Kids pattern to date. With the option of sweats, shorties, and shorts, this pattern is perfect for all seasons! It comes with the size range of NB - 9/10. This pattern is perfect for those just starting out. It's also perfect those who have been sewing for a while as they are extremely fast to put together with adorable results.
I love to use french terry for the pants and shorties. Any knit fabric will work though. For the waistband and cuffs you'll want a fabric with a lot of stretch and recovery. My go to is 2x1 rib!