I'm making a shrug for my friend's 3 year old daughter. It's a surprise for both of them, so I can't ask my friend her daughter's measurements. I used this website for most of the measurements http://www.yarnstandards.com/headsize.htmlI have it all figured out except for the upper arm measurement. I couldn't find it on the site. So I am guessing 6 inches, so 8 inches for the sleeve. Does that sound about right to anyone?
Gosh, it's been so long since I've had access to a 3 yr old!
Do you know what size clothes she wears in general? If you know she buys size 4T (or whatever) size, you could measure a shirt or sweater in the store.
Measuring a garment would probably be better. Can you ask her mother to measure something she wears?