It's no biggie. With as much time as you have, you can walk between any two terminals without leaving security. But to avoid a long walk, you can ride the new train, which runs airside of security, and which affords great views of the airport.

The kids will love it.

Max ride time between stations is 9 minutes. But if you have time and the kids are into it, you can ride an extra full loop around the airport in 20 minutes.

I think the warning dates back to the old train system, which was very slow and a hassle.