We have always done late so not sure what early is even like. We have skipped MDR and gone to the late show (the one early diners go to) and we did notice quite a few more small children than when we did the 6pm show on the same cruise, so I'm pretty sure there are going to be less kids in the late seating. Less, but still several. Not that this would be a reason for choosing one over the other, but for some, that may be a deciding factor.
Disney has really improved the last few years with leaving things open later for those who are late seating and may want to go do something after dinner. Yes, there have always been the adult lounges, but sometimes we like to dip in the hot tub or something like that. That's really the only thing to watch out for. We like to do something after dinner. Late seating means we go to the show (if we want) and then dinner. Then after dinner we go to one of the clubs (usually comedian). With early seating you'd be going to dinner, then a show then another show?
Also nice to just take a walk around the deck in the moonlight after dinner.