If they seem to be getting too hot (panting hard, drooped wings, sitting around) you can dip their feet in a bucket of cool water for about 5 minutes. It helps.
I also do this, except I use scraps from smoothies I make for myself! Just put it in a cup and freeze it in water! They don't eat the ice, but the fruit is nice and cold!and the frozen fruit mix from Walmart. I put the frozen fruit in a big bowl of water and freeze it overnight, then put the big frozen mass with them in the daytime. A nice, cool treat.