In July when we went, our kids were 3 and 1. We did the EMH mornings only at MK and AK. They both worked very well for us. Both mornings, the park opened at 8AM instead of 9AM, and we arrived between 7:15 and 7:30AM...not a problem for us as we and the kids are normally early risers. We did leave the park by 2PM at the latest, even the other 2 parks on the non-EMH days because it was hot and we knew the kids would need that afternoon break.
I will tell you one thing...we did EVERYTHING we wanted to AND THEN SOME!!! DH never thought he would get to ride Expedition Everest at AK, but he did! We were there for early morning EMH, rode the safari first (in the first vehicle of the day!), then I took the kids into DinoLand USA, grabbed FPs for Dinosaur while DH went and rode Everest. The kids enjoyed more of the kiddie stuff in DinoLand (no lines!), then DH met up with us at Festival of the Lion King...we arrived there at exactly the same moment but coming from different directions, it was actually kind of funny. We saw the show and loved it! It was a 10AM show I believe (we of course had arrived early). We then went back to Dinosaur (FP time was up) and took turns riding (kids are too little for it)...then we went to Flame Tree BBQ for lunch. There is one example...we did do a few more things after lunch but left that park at around 1PM. But we did everything we had planned!
At MK...we went straight to Fantasyland for the kids as soon as the park opened (we had gotten there at 7:15AM). We walked right on to Winnie the Pooh, Peter Pan, Tea Cups, Snow White, etc. We had done everything we wanted to and the kids wanted to in Fantasyland by 8:20 and still had 40 minutes until regular park opening when we were going to head into Frontierland for Big Thunder. So we decided to go to Tomorrowland and my older son got to do the Indy Speedway which he loved (still talks about it!). We walked around, took another walk through Fantasyland and had a very nice hour overall, seeing more than we anticipated. We then headed to Frontierland at rope drop, and by this time (9AM), there was a 40-minute wait for Peter Pan! We were so glad we had already gone on it! We went to Big Thunder, I rode then DH rode and I took the kids to the little play area near Splash Mountain. Then we went into Toontown and my older son rode the Goofy roller coaster twice...VERY short line! We eventually made it back to Tomorrowland. DH had a FP from the morning but we had some time...we went to Cosmic Ray's for lunch and did the Carousel of Progress. Then DH went on Space Mountain. That ended out day at MK. It was around 1:30 or 2PM at the latest. We headed back to the room, then returned to MK for a 6PM dinner ADR at Crystal Palace, looked around some of the stores on Main Street and enjoyed more relaxing time at the park before heading back.
We had a great EMH morning experience. Would do it again in a heartbeat, but only if we got there just as early. As my kids get older we would probably take advantage of evening EMH, but only if the following day was a day off from the parks.