We always have the park hopper, but rarely use it. The reason being is all the time and effort it takes to move from park to park with little kids. Even though Disney makes this as simple as possible, it is still quite a process. We really only park hop when we finish with AK and head to MK for something special - like Spectromagic. This works well because Spectro is not shown every night and is a must see in our opinion. Or if we have had a couple days in MK and want to see fantasmic, or eat at one of the amazing places in Epcot, we hop. Other than that, we try to stay put in the park we chose that AM. We really try to plan around the crowds, plus we go in "off season" so the parks have shorter hours, so the hopping wastes a couple hours in all ready limited time. To leave a park, return a stroller, get the bus to the next park, load the kids, travel to the next park, make it to the gates, go through security, go through the turnstiles, get a new stroller and decide where you are headed I just think is too much. I once timed what it took for us to get to MK after a day at AK (remember you bus to the TTC, catch the monorail or ferry and then enter MK), it was just under 2 hours from the time we decided to head out of AK to our first thing in MK. It just takes time, so don't under estimate it! Plus, that is going directly from park to park. Oh, I should give one more exception. We always hop between Epcot and MK - with both on the monorail, it isn't a big deal. Plus, the air conditioned ride is a nice heat break!
I am a real advocate of not taking an afternoon break (unless you are staying at a resort on the monorail), but only going to the parks every other day. Let the kids swim, nap, and get to bed early on the day between the parks, then hit the parks and spend the whole day there! We have always used this and find it is the best plan for our little family! Have a great time!