We started small in MK, like they went off to ride Space Mt, while we did a different ride or whatever, then meet at a certain familiar spot. Also one of the first times, was letting them eat in Pizzafari, while we ate in Satuli. Got them all set up at a table there, then we left. They met us later in Pandora. Last year, let them go around in the WS at Epcot, since they wanted different food than we did. I want to say DD was 14 or 15, and DS was 12 or 13. They each had phones, w park maps, etc. and were familiar w the parks...still got turned around, and took the scenic route we'll say, but found us. Last year, for the first time let them leave from Boardwalk and meet us in Epcot. I was a little nervous about this one, but they did ok, and we texted all the way. DD is VERY petite for her age, and was questioned about how old she was when entering the park. While I am comfortable letting them go around parks, I'm not comfortable letting them walk around hotels/resorts alone, together is ok, but not alone. In general, they do not get along all that well, but they do when they have to. We're going to Universal next week, and I am anticipating a lot of splitting up. Debating if we're going to let them walk or take boats back to the resorts w/o us. We'll play by ear. I say start off with a familiar park, and give them a time to meet/check in often.