Thank you guys so much for your responses! I actually have great children who happen to not be good holders on to things. Frankly my husband would never wear a fanny pack (no offense really, it's him not me) and he wouldn't let my son wear one either. He would help hold a backpack of course it's just cumbersome. My dd8 would absolutely carry one but she is really small and the kid sized one I bought doesn't even fit her glasses and the full sized one won't even fit around her waist. I understand what could and should be done I am simply asking if anyone has or has thought of doing what I am thinking of doing. I hope this doesn't sound unappreciative 'cause its not just living in my reality where i can't afford to buy new drinks every hour, have very fair children who would probably self-combust without regular liquid and am trying to find a way for them to have fun without spending all day running back to this store/ride where they left this, that and the other thing which happens all the time in my world (when they use drawstring bags). Again, not going back is certainly a solution which we have employed in the past but it does not seem to alleviate this issue they have and only serves to ruin a nice afternoon.
OK, OK, where to start. Have a look at rei.com. Many waist packs are serious pieces of sporting equipment. They need not look like purses on a belt. Consider the ones that are worn on the small of the back and have separate water bottle holders on each side.
Everyone needs to carry their share. I know we parents will always carry some of the kids' stuff. The goal is just not to carry it all. To this end, everyone's waist pack or backpack should be relatively small. Don't take what you might need, just what you will need. (Of course, I also take stuff that I hope not to need but it would be so awesome to have if... Yay, yay, I'm a boy scout. Can't go anywhere without a small first aid kit.)
Smaller kids almost always do better with a backpack than a waist pack. Just limit its size to hold a light jacket, a small bottle of water, sunglasses, a favorite toy and one bag of snacks. (Let dad carry the $1 ponchos and glow sticks from home.)
By the way, you need not carry a lot a water. You can get filtered, nice tasting water with ice from any counter service restaurant for free. (A lot of people don't like the taste of the water from the drinking fountains.) If you use small 8 or 16 oz bottles, it's not a lot of weight. If you don't like plain water, you can get individual packets of tea, gator-aid, kool-aid or lemonade to add to your ice water. I agree that you have to stay hydrated. This is a fairly cheap way to do it.
I know leaving bags behind can be a problem. For us, since everyone has one, everyone is keeping an eye out. We usually don't get more than a step or two away before some says: "where's your bag?"
You said you have very fair children. Don't forget hats and sunblock, even on cool days.
(ETA: Hey WDSearcher, great post. I guess I need to type faster.)