You can find a free pattern and tutorial for making a pair of baby leggings over at I Still Love You. They’re quick to sew. Her variation avoids threading elastic through a casing and uses banding at the ankles in place of a hem. The pattern is in a size 9-12 months. If you need to make leggings in a different size, you could trace a pattern from a pair that fits and then use the tutorial as a construction guide. Get the pattern and tutorial.
[photo from I Still Love You]
[via One Pretty Thing]