At times, I'll use a well-fitting top to create patterns for my kiddos' clothes. However, more often than not, I make patterns off of measurements. I just kind of think it's easier. And when you get a basic pattern done, it's super easy to jazz up.
Disclaimer: I am in NO FREAKING WAY a pro at this. This is just what I do for my own patterns that works out well for me. :) I also feel a little like I'm reinventing the wheel here. There's nothing new or ingenious. But I also feel like it's helpful to have a kind of checklist, especially if you're just starting out on kids' clothing.
To make a dress or top measurement, here are the digits you need to get:
Waist (you may NOT need this one, just so you know, unless you're doing a drop-waist. For Riley, who's shaped like a pencil, her waist and chest are nearly the same)
Chest: measure around chest, under the arms
Shoulder: measure from side of neck to edge of shoulder
Sleeve/arm length: from shoulder to desired sleeve length
Top/dress length: from shoulder down to desired top/dress length
So here's a picture of a pattern I just made this morning, based off Riley's measurements. You can see the measurements for both girls in the top left. Then you'll see the inches added for inseam and a little fudging room. (Click to enlarge!)
Use your measurements to kind of play connect the dots and ta-da! I made this one an A-line, slanting it out from under the arm.
**Ignore that "add 7 inches" note. That's for my next tutorial. :)
Now that you have the basic pattern, you can adjust the length, neckline... just play around. Sweet, huh?