^ What kind of idiot, other than a blindly partisan zealot who would rather make a cheap political point than keep their kids out of harm's way, brings their kids in strollers to a demonstration led by a group with a history of attracting people with masks, and wielding baseball bats while carrying bags full of bricks and rocks? You can't blame the horses or the officers on them if they were responding to the violent provocations of the cadre of violent agitators that form the core of many of OCAPs protests. If anything, the horses prevented the situation from getting worse as they are used for exactly the sort of crowd dispersal you describe. That's what they are used for, and why they now wear shields over their faces and legs because those very protestors either kicked, stabbed or tripped the horses' legs or threw marbles under them to try to trip them or disorient them. Then see what happens to those old people and kids when that takes place, and those "weapons" as you call them, are unable to do what they and their handlers are trained to do.
And to answer your question, horses are often used for several reasons. One, is that if you've ever seen them, they draw a crowd, especially kids. What better way to foster better relations than to have officers seen on a horse, rather in a car. The second is that horses can traverse areas like parks and ravines better than officers on bikes can. And with the snow on the ground, horses are ideal for that sort of thing. Personally, I hope this POS, if he's found guilty, gets the severest penalty they can find. It wasn't as if he hit them accidentally. He deliberately circled back, and just rammed that horse. The officer riding him would likely have been killed as well if the horse hadn't taken the brunt of the impact.