He shouldn't be getting kool aid at this age. My child is almost two and a half and still has not had kool aid, there is no reason to give it to her at this age (sugar + artifical flavors + artificial colors = ick!!). We still water down the apple juice and orange juice she gets on occasion.
All the sugar in kool aid and sodas and sports drinks, etc., can really disrupt their renal systems at this young age. It's like a diabetic not being able to regulate their blood sugar properly.
Keep offering him breastmilk/formula if you think he's getting dehydrated from the heat. When you know he is full-- offer him little tiny sips of water from your own cup, or a small cup. That's all he needs at this point. He may need it today, as he lost some fluids yesterday.
Call the pediatrician for more advice on what to do when it's very hot out and you want to "refresh" him.