Wasd your child trained to cyucle on the road or dedicated cycle path, footway cycling is illigal,
was your child wearing a helmet,
did you have proper control of your child and was he kept in sight at all times for a child of his age,
was your child wearing relevant hi viz clothing.
all questions an insurance jobsworth will ask to try and put you off claiming, thats if the dog owner had any insurance to defend.
Had a similar incident last week with an out of control dog, the dog owner starteds creaming abuse, i just rode on and pointed out to the numerous witnesses the dog was out of control and so was the ownner and to avoid him, this made him more angry as i rode off and his dog ran the other way.