Hi! Here are 2 answers for you:
1. According to the Patternworks baby blanket challenge benefitting this organization, blankets should be 29-32" square, at least that's what the rule is for those participating.
2. Check the free crochet patterns on this Newborns in Need site, as I found there a pattern for a baby afghan or blanket which gave different measurements according to the baby's size.
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.