The picture idea does sound cool; I need to get ds8 a camera, he has taken a lot of good shots with mine and I think this would be another good outlet for such an arty guy.
Plus, even if he's at the sitter's I might get to 'see' more of what they've been up to.
Here are things I thought of:
Strawberry picking.
Rocket launching.
Going to a mall that has a climbing/play area (if your 6 year old is not too big yet)
make ice cream
or ice pops
make sun tea or lemonade (lemonade stand)
we found a great book called 'totally irresponsible science', it mostly uses stuff you have around the house already.
wash the dog
make an oven out of a box+aluminum foil - cook an egg (check out online - your summer temps sound perfect for this)
playgrounds in the early morning, swing in a hammock in the afternoon
set up a tent in the backyard (under a tree if possible for double shade) - great for toddlers!
We did lots of these things when we were in tx with our then 4-year-old.
