I made these Halloween Pajama Pants last night on a whim in about 40 minutes! I just made them using the simple method. These aren't the best instructions ever, but they're all over the internet. This is just my interpretation of what I did.
1. Got a pair of my daughter's 18 month old pajama pants.
2. Folded pants and fabric in half and placed them on fold of fabric, minding the fabrics pattern.
3. Cut about an inch around the pants on the fold. (I left about 3 inches on the top of the pants to fold elastic into. Depending on how stretchy your fabric is, you could have a small top hem.)
4. Pinned pants together right sides in.
5. Sewed up top sides.
6. Pinned the pants of legs. (This creates the arch you sew along next. Top seams will now be in the middle of the pants. Leg seams will run along the insides of legs.)
7. Sewed along the legs of the pants. Sew top hems down in the same direction.
8. Fold top of pants twice for a nice, comfy fit. Using about a 1" seam (or whatever you prefer) sew around top of pants, leaving a 1" space for adding elastic. Measure your elastic to baby or to original pair of pants, then insert elastic by attaching a safety pin to one end. Run elastic through pants, then sew ends together.
9. Now you can finish the top of the pants and close that 1" space.
10. Fold leg cuffs up to desired length. (I folded mine twice to get rid of that raw edge. Some fabrics might be cute with a raw edge and not even need folding!)
11. Sew cuffs in place.
12. Find an adorable baby to stick your Hallloween pants on and take some pictures. Mine was asleep at the time.
Using this method and some altering, I made a pair of pants to fit a 6 month old that fits into 12 month clothing and a 23 month old that wears 18 month - 24 month clothing.