The waist in most 12 month pants are still too big for her, but they are getting too short. I can't go up to 18 months because they would swallow her whole! So what do I do?
Add a ruffle to the bottom for length!
Step 1: Measure the width of the bottom of the pants you are using. Multiply this by 2. This should give you the total width around the bottom. Now, you'll multiply this number by 2. This will be for the fullness. This will be your W (width).
Step 2: How much length do you want to add? In this example, I wanted to add 3 inches to the finished length, but I was positioning the ruffle an inch above the bottom of the jeans, so I added 3 + 1 + 1.5 (for finishing)= 5.5 inches. I didn't want to finish the bottom, so I doubled this so that the edge would be a fold.