Reactive dog owner here who can offer some impartial insight.
For context, I have a GSD X Staffie rescue who is super reactive to other dogs, though he loves kids and babies.
First and foremost* *I just want to say I hope your baby is okay and safe, and that no injuries were caused to anyone in your family. I can totally understand how scary it would've been to see a dog run towards you if you're unsure of the temperament or what the dog might do.
I can also understand that your DH's reaction may have been spur of the moment or kneejerk...
I would also like to add that the dog owner in questions sounds like one of many absolutely trash owners who have no respect for others and their safety.
My boy has had a very hard life and has suffered through lots of abuse and abandonment, and has had a few different families before ultimately being adopted by myself. I have taken him to multiple behaviouralists, but really none were that effective and he is still a reactive dog so as a result, anywhere I go with him, I ensure that he is safely restrained and on a lead at all times, no exceptions. He is never let outside off lead and he is never unsupervised by himself outside of the home, even in our back garden.
Unfortunately, a lot of people these days are really lacking the skills, intelligence and initiative to look after a dog properly and they do not adequately take care of them, nor do they care how their actions affect others.
BUT, that said, kicking the dog was absolutely not correct at all. You didn't say anywhere that the dog was being aggressive, attempting to bite you or any member of your family, nor did you specify that you or your partner tried to give a clear instruction or demand to the dog, so I'm intrigued as to why that would have been the first course of action?
Not only was that unfair to the dog because, ultimately it's not their fault that their owner is an inconsiderate dickhead, but also, likely could have also further provoked them and possibly inflamed the situation even more and made it potentially even more unsafe for you all.
I hope that you had some serious and unsavoury words for the owner, though.