I've lived and learned with the sewing thing. Sometimes, no matter how well you take measurements, a garment sews together with a completely different fit than you expected. Although it's an extra investment in time and effort, it can save a world of heartache (and a small fortune in fabric) to make a practice "muslin". It's true for formal wear, and it's true for costumes.
That's why I just sewed two paisley bodysuits.
They're unfinished, natch. (And FTR, they're paisley because I am a frugal goddess and repurposed an old bedsheet.) But look at the difference in size, between ONE grading of size in a prepackaged pattern (Simplicity 2855, a perennial workhorse. About 30 years ago, my mother used this same pattern to make a costume for yours truly. Ah, memories!). And I'm *so* glad I did the test-run, too, because as I'd suspected...I'm going to have to use one (the smaller, it turns out) as a starting point but alter the snot out of it to get it to fit my kid correctly.
Seriously, between two sizes we have a four-inch increase in the torso length, another four inches around the waist, a SIX inch increase in the sleeve length, and only two inches in the leg.
Whose kids are they measuring? That's just crazy!
Anyway...stay tuned. This is just the framework for a costume I'm going to be freehanding on top of this base. Wish me luck!!