As well as parents educating themselves and their children about dogs, some dog owners need to educate themselves about children.
Young children in particular are not robots anymore than dogs are. Their behaviour can be impulsive, uncontrolled, erratic and illogical. Despite attempts at 'training' by their parents.
So your dog that is lovely, calm and well behaved in an all adult household may behave very differently around young children. A young child won't necessarily have the knowledge, awareness and control to behave appropriately all the time around dogs. Its unreasonable to expect them to, however hard their parents try, especially in public places.
So don't just stand there with your dog and say: "Don't run away he thinks its a game"
"He's never done that before you must have scared him" etc.
If you're in a public place and there are young children, the only sensible thing to do is keep your dog under control.
Thinking about it, dogs and young children have a lot in common, in theory they should get along very well :)