I have two sons aged 6 and 8 years, they have been brought up with more than one dog in the house, and their grandad has a dog who visits regularly. My boys know that they do not approach any dogs in the street/parks etc even if they have seen the dog several times and know it is friendly, you never know when or what would make a dog turn, this could apply to your own dog aswell, my boys have been taught from a very young age to respect our dogs and treat them nicely. They know that when a dog owner says "it's ok to stroke my dog, he's friendly" they dont touch it until we say yes.
In this day and age, respect for all animals should be part of general growing up for all children, it would save lifes and unjuries to children, and adults, and unnecessary upset for dog owners whose dog may have to be put down. I never let my dogs off the lead, I am scared they would run off, Charlie regularly has selective hearing and I am too fat to chase after them.