I am very hesitant around small children that I've never met before. Once, a mother and her 2-year-old boy came up to my golden retreiver, Tigger, and asked to pet her. I said it was all right. Imagine my shock when this child YANKED my golden's ear and poked her in the eye! It was hard enough to make poor Tigger shriek with pain. Mom immediately stopped the child and apologized profusely, but the damage had been done. Tigger never again trusted small toddlers. She would keep her distance from them, and growl if they came too close. No matter what I tried to help her, she never overcame that distrust.
I will let small children pet Zeus, but I stay right next to Zeus and get down to the same level as the child. That way, I can immediately stop the child if it even looks like they'll try to do something unpleasant. I understand that toddlers don't realize what they're doing, but that doesn't mean my dog should suffer the consequences.