Seeing not much response to this message, I'm just passing along some information gleaned from our local children's hospital. About the yarn, it seems to be best to use acrylic, as quite a few babies are allergic to wool and even to cotton. You can find quite a lot of info about sizes by checking the free patterns available for knitting and crocheting on this website. I've already copied several patterns into my computer to use as references when designing caps, socks, etc.
This is my first day to learn about this organization, but even a newby can say welcome, and thanks for also wanting to volunteer!
Donations are always welcome. Please contact the chapter closest to you and share your thoughtfulness so more babies can be reached. You may find a list at www.newbornsinneed.org. Look for the link at the top of the page. Want to contact our main offices? Reach out to nationaloffice@newbornsinneed.org. We love to hear from our volunteers.