Photo Id is not a bad idea for travellers of all ages . For those of you who are US citizens
(including the kids) the best photo ID in the world is a US passport. It's easy to get,inexpensive, good for 10 years(kids 5years). It saves all the hassles of birth certificates, other photo ID's etc. Get one for all your family members and then forget worrying about what kind of ID to have for what kind of travel.