I'm sorry but why everyone including you is blaming your dog fully, I don't know. A person could have been standing outside holding the dog and the result could have been the same. Some uncontrolled small child, that charged out the shop (not under control from the parents) must take some of the blame surely. 🙄
Imagine this... your friend is standing outside the shop on his own waiting for you friend who had popped into the shop for an item. Your friend, minding his own business is suddenly rushed at from someone coming out the shop, no warning, a stranger unknown to him. What would you expect your friend to do... defend himself, push the person away, or allowed himself to be potentially hugged or even attacked, by a random???
Would you be berating your friend in this situation, if not why is it different?
Your dog didn't attack the child, your dog was suprised. Your dog jumped up at someone who entered his space without warning and they made contact, not a bite. Clumsy child meets dog. 🤷🏽
Both you and the parent needs to take is as a lesson and you stop berating your dog and leaving it outside shops. Your dog was being a dog. It is your job as a dog owner, to not put it in a position it may feel threatened.
Some children need reins as the parent is not always 'eye on' and the child does things like this. It happens. It's not as big a deal as you're making it out to be.