Well, I must say, I think I have the ultimate kid set up. I have 3 little boys, 7, 5, and 2. It goes without saying that I would rather hang out with them then anything else, but the close second is rolling through a willing school of ‘eyes!
I have a portable DVD plyer for the boat that bridges the lapse in time. This little setup has allowed me late nights on Mille Lacs, overnights on Ottertail and day trips all over SW MN and SD. While I have some reservatons about electronic entertainment on the water, my boys love riding in the boat and talk about the fishing with excitement. My 2 and 5 yr olds harrass me to take them fishing constantly and MOM has a hard time saying no! (A huge bonus) 
The 7yr old has a gameboy that he brings and, of course, I always make sure there is LOTS of food and drink on board.
I have a bag of bags (Walmart, Target, etc) for poop and garbage!
I pack a 5 gallon bucket and one of those trainer toliet seats (keeps little ones from falling into the toliet) that fits perfectly on the pail. All 3 somehow need to poop when we get out there!
This summer the fellas enjoyed stripping down to nothing and sitting in the livewell “swimming” and generally enjoying themselves.
I cut down a piece of PVC to hold a 62″ golf unbrella for shade and always bring matchbox cars.
The key here is the kids. I agree that when they want to go, its time to go, but with a little extra stuff, you can increase your water time to almost as long as you can stand it! On the boat almost anything goes but KEEP CANDY TO A MINIMUM to NONE if possible……not too much needs to be said on that topic….. 
I will be on the Mille Lacs on Sunday so keep your eye out for the glowing Blue Grestliner with 4 happy boys on it! 