Firstly, the 'not all dog owners are the same' is meaningless if you're out on a country walk with your boots covered in dog shit. 'We all pick up our dog's poo'. No, you don't. At a local beauty spot which is great for walking, dog walking, taking kids out into the countryside, the local authority decided to spray all dog poos with fluorescent paint to highlight them. Jesus, it would make your stomach churn - there were steaming piles of dog shit EVERYWHERE. Sadly, these 'few' are a lot more than the 'few' you would like to think, sadly.
As for the dog jumping up at a small child, scratching them and knocking them over. SHAME on that dog owner. If you cannot control your dog off the lead you are an irresponsible twat and you shouldn't own a dog if you cannot figure out that they might do this to a small child and that that isn't ok. It's completely, totally unacceptable.
"He's only being friendly" - good grief, how utterly stupid. He's knocked someone over and they actually think that's alright? Because he's 'friendly'!
If you cannot control your dog, consistently, by voice, off the lead, don't take them off the lead. You only have to go round parks where dogs are off lead and all you hear is 'Rover, Rover, Rover, come here, ROVER, COME HEEEERRRREEE!' whilst said dog completely ignores them.
How utterly irresponsible of the owner of that dog OP, I'd have been absolutely **ing LIVID.
And I say this as someone who has been animal mad from a young age and still am. I absolutely love animals. But how they interact around humans, especially children, should be a paramount concern of all dog owners.