Hi Ivagrove,
Use a bedding that prevents the bunny from burrowing and remove some ofthe fur in the nest so that air can circulate through it.
Provide plenty of water to the mother, a fan on low if you're able togive them one, and iced bottles of water (like a plastic soda bottle)so that the mom can lean up against it if she's too hot, and it mayhelp to cool down the temperature a bit. Keep the rabbits ina shaded area, as you know.
Take a look at the post above, "Keeping your rabbit Coolin the Summer months" for more ideas.
-Carolyn