I know it's not summer anymore but I just had to let you know about an awesom product I came across online a couple years ago. It's called Cold Seat.
It's a frozen car seat cover you but on your childs carseat in the summer time. Like if you go to the mall or somewhere for a long period of time, you put this frozen cover over your child's carseat before you get out so when you get back in the car, you don't have to worry about the hot seat burning your childs legs. This product is worth it and I would buy it all over again. Check it out!