I read this: "Children who are age 6 through 11 as of the date on which the exchange order is issued are eligible for child PASS prices. " (at http://www.japanrailpass.net/eng/en003.html (types and prices))
My daughter is 11 years and 10 months. On the date of our trip to Japan she will be 12. Is she eligible for a Child Pass if the exchange order is issued before she turns 12?