Wow, you've had more than your fair share of encounters with badly behaved dogs! The shame of it is, every single one of your examples are down to an absence of training. Dogs do what they are allowed to do.
Jumping up is an absolute no-no in my book. It's always been one of the first things I've taught my pups. It's completely unacceptable for a grown dog - more so a wet, muddy grown dog - to be jumping up at anyone and especially a stranger. Well done you for correcting the dog, I would have done the same. Unfortunately, some dog owners allow it when they have a small, cute puppy and strangers are willing to overlook it but then find 12 months later that jumping up has become a massive problem because (surprise surprise) the dog is now a fully grown, muscular, very powerful adult dog who is jumping up, dirtying strangers' clothes and bowling them over. It's no longer "cute" behaviour. If only they'd taught the dog not to do it when it was tiny.
As for jumping up at prams and snatching food from babies, words fail me. What the bloody hell?! In my book, this is getting into the realms of "dangerously out of control in a public place" which is an offence under the Dangerous Dogs Act. Again, it's down to a complete absence of training and allowing dog behaviour which is clearly highly unacceptable and potentially dangerous (small hands, sharp dog teeth.) If I was walking past with my dogs and witnessed that, I would have called the owner out on it.
Idiotic!
I take your point on multiple dogs. At one stage in my life, I had 3 Border Collies and one Black Labrador, of different ages. All four dogs were advanced obedience trained and two of the Collies were also agility trained. I invested a great deal of time, energy and money into my dogs so that they were an absolute pleasure to own and not a pick of bother. However, when it comes to owners who lack control over one dog, it's mind numbingly obvious that adding a second or third dog to the mix is not going to be a good idea. They'll simply end up with two or three dogs, all of which they lack control over.
As a rule of thumb, when you hear the words, "he's friendly" there's one of two likely outcomes. The first is he isn't friendly at all as evidenced by his hostile body language, barking and/or growling, usually at my dogs. The second is he is friendly but he's a lunatic: jumping up at humans, jumping on the back of other dogs and generally being an anti-social nightmare.
On either front, I put on my harshest tone of voice, make some sweeping arm movements and chase the dog back to his owner. Invariably, the owners don't like me telling their dog off but usually, as you say, they're a distance away or busy on their phones so I take the view that as they're unable or unwilling to control their dogs, I will do it for them.
I find it very sad that both of your children have had negative experiences of dogs which still effect them. Those situations should never have happened.
As you said at the beginning of your reply, it's only a minority of dogs which are allowed to behave badly, the vast majority aren't a problem at all. The trouble is the minority give ALL dogs a bad name which is the reason why I - and I suspect other owners of well behaved dogs - will call out bad dog behaviour when we see it!