Yes, you prepare for the heat by training in the heat. Shorter distances at a time. Pouring water on your head, and everywhere for that matter, is an awesome way to keep cool. Feels SO good to have even the hot breeze on you as you ride when you are wet. Keep an extra bottle of just water. On longer training rides, plan where you can stop and refill your water bottle. Could be a park with a drinking fountain, a hose ... maybe a McDonalds or Gas Station where you get fountain drinks ... only just fill with water. Or buy bottled water. On an organized ride refill your water bottle at SAG stops and douce yourself while you're at it. Makes a big difference. You might carry two bottles with your sports drink on your bike and a water bottle in your jersey pocket.

I just did a club ride yesterday in hotter weather than I've ridden in all year. Wasn't fun. I did okay, but not nearly as well as I usually do. I lost the group I was with on a hill on the way back and finished the ride by myself, cutting out the last climb. This never happens to me. The heat definitely affected me. It can be mentally depressing, but I have to remind myself how well I did just a week before.

Good for you for teaching your kids it's okay to not reach a goal, but to keep working at achieving it. It's possible you might have been able to finish had you pushed yourself. But you also might have suffered heat exhaustion or heat stroke (are those two different things?!). All you can do is listen to your body the best you can. The more you ride, the better you'll know what your body can handle. Better safe than sorry. I was a spectator at VERY hot L.A. marathon my dh did a few years ago and watched a runner fall over right in front of me. Paramedics came to help him. You could hear sirens all day as runners were continually affected by the heat. You may very well have done the smart thing. You'll learn from this experience and be a better and stronger rider for it.