Could you just keep a cooler in the truck? Then you could add freezer packs and extra (filled) water bottles each day. (or even freeze some of the water bottles) You could get 2-3 extra water bottles per kid. This way you wouldn't have to deal with filling them. Kids could just grab a new one when the old one is empty.
Tara
living a crazy life with 3 boys
I am thinking now
of grief, and of getting past it;
I feel my boots
trying to leave the ground,
I feel my heart
pumping hard. I want
to think again of dangerous and noble things.
I want to be light and frolicsome.
I want to be improbable beautiful and afraid of nothing,
as though I had wings.
~Mary Oliver