A few weeks ago, a new mother complained about the variation in infant clothing sizes. She explained that her 12 month daughter wore clothes ranging in size from 6m to 18m. Some marked for 12 months were either too big or too small. Finding clothes that fit was a matter of trying things on a fussy baby.
She stated, "You can't trust what the size tag says."
Kathleen at Fashion-Incubator wrote an article about problems with sizing studies, especially for women. Children's sizing studies present some of the same difficulties. Children's sizing is complicated by the fact that children grow and at different rates. Ethnicity plays a part in proportions, weight, and growth rates. As a technical designer, I feel that I am only taking my best guess when drafting patterns. I have to synthesize about a dozen different size charts and methods to come up with something that works and fits! I firmly believe that even infant children deserve clothing that fits.
My major issue with most measurement charts and sizing studies are that they are minimally useful for patternmaking for infants. Many measurement size charts either completely ignore or present limited info for infant sizing. The Armstrong book starts her charts at size 2/2T (some of her measurements are a bit funky too). The Gloria Mortimer-Dunn is the same way. Childrenswear Design, has some basic information for infant patternmaking although the information is not complete. The best presentation of measurement info is from Winifred Aldrich in her book Metric Pattern Cutting for Children's Wear and Babywear: From Birth to 14 Years .
I have drafted basic blocks using Aldrich's charts and instructions. They turned out ok, but definitely needed refinement for style and fit. I thought the basic, fitted blocks need a little more ease and a lower neck. The flat blocks needed a better armhole shaping. Despite that, with some tweaking, you could have a nice set of infant blocks to work with. Part of my difficulty could be that the British are accustomed to a closer fitting block and the metric system. I had to wrap my head around metric conversions, which probably introduced some inaccuracies.
I haven't talked much about measurement charts available from ASTM. This is because I have not purchased a set of charts from them. I don't have the need at this point. Other government studies are interesting, but don't contain enough of the measurements needed to draft basic blocks. Growth charts and retail size charts (and a few in patternmaking books), list infant sizes by pounds and lengths. Those are interesting for comparison and not useful for drafting patterns.
I am not sure what new childrenswear designers are to do. Most companies develop their own measurement charts and some are better than others. Getting those first, good bodice block patterns are critical because every future design is based off of them. It may be easier to drape your first blocks off of dress forms rather than drafting from measurements. Or maybe a combination of both. This sizing study problem could explain why infant sizing is all over the place.
Over the years, I have settled with basic patterns that have proven to work. They continue to be modified for improvement and someday they will be what I hope is a great pattern.