Consider whether your child and you can handle it. Burning Man can be very hot, very loud and very crowded. If your child is too young to talk, it might be an experience neither of you can enjoy. Even older children who don't do well with crowds, heat, or roughing it might not have a good time.
Take plenty of supplies. Packing for Burning Man is an involved process anyway, but you have to be even more thorough if you have kids. Having enough water and easily portable snacks is particularly important. Check out the Burning Man packing list links below for more information.
Set up places to meet in case you get separated. Wherever you take your child at the festival, make sure there is somewhere within view where your child can meet you. Keep in mind that kids are little and can't see as far as you can, so pick an object that both of you can easily spot.
Always outfit your kid for the day. He should have sunblock and/or protective clothing, and a backpack with plenty of water and snacks, a map, and a flashlight. That way, if you do get separated, your child will have the tools he needs to keep his energy up and find his way back to you.
Make sure that your kid knows what your camp is called. Consider making an ID necklace for her with her name and the name of her camp. That way, she can always ask for help finding her way back to the correct camp.