Much depends on the kids and their experience with the parks. My two practically grew up there, and my DS was running around loose on his own inside the parks from age 10, and has been on his own to get back and forth from the resort since about age 13. (He usually meets us for meals if we're in the same park, because after all, why pass up a meal that the 'rents will pay for, LOL!) For my kids, the Disney parks are not confusing at all, they know them like the backs of their hands. DS has been taking his younger sister into the parks on their own for a while now.
The 14-to-enter rule is a very recent change (March 23, 2013) before that the age was 8 (I have it printed on the back of an old ticket that I saved.) It's very much about
Disneyland and the Disneyland-summer-daycare issue. About 10 years ago I was in Orange County, CA for a convention in June and decided to do a day at DL on a weekday. When I walked over in the morning there was a row of minivans as far as the eye could see pulling up to the drop-off entrance. I happened to leave the park at about 6 pm because I had a dinner to go to, and there were at least 200 kids, many of them pre-school aged with older siblings, sitting on the sidewalk there waiting to be picked up.