Honestly, everything we used was a very temporary fix. Really, the only thing that truly cooled us down was being inside the air conditioned attractions/restaurants/stores. The MK was the best place because there is so much in and out in that Park. The heat bothered us the most at HS and WS in EPCOT.
If your children are stroller riders, I would defnitely get the very best stroller fan available -- maybe two! Those kids in strollers looked SOOOOOOO HOT.
Good luck and please, please, please don't stress or spend hours searching for the perfect "keep me cool" tool. I'm here to say that I did just that -- hours and hours on these boards,
Amazon, and all over the web researching fans, misters, chilly pads, you name it! -- and, in the end, none of it really saved us like I would have hoped. The fans helped the most and being in AC like I mentioned.