For whatever it's worth, both of my kids (age 5 and 7) were randomly selected by the computer to be searched on the way to WDW 2 weeks ago. TSA told us that kids are not searched, so they searched my wife and I instead. They did not ask for any ID on the kids. If they were checking for children's ID's, I'd think that ones singled out for a search would need them, which we did not. I've never heard of anyone actually having to provide this for a child. Most people don't have it with them at the airport, so what would be the point?