The Riverfront is EXTREMELY hot in the afternoon so try to go to Fan Fair X or other indoor activities during the hottest part of the day. I witnessed three people pass out due to heat exhaustion/stroke and be hauled away by EMS within an hour one day.
If you are going to brave the heat make sure to stay hydrated! Drink lots of water even if you aren't thirsty.
There are also cooling towels/neck wraps on the market that work really well too. You can check them out by clicking here.