It wouldn't matter if you have horses or not, if your kids go barefoot and step on something rusty, tetanus is always a possibility. It's not because of the horses. (my kids go barefoot, too. They're supposed to, they're kids!)
Hmmm, about the strangles, I'm inclined to think that your daughter getting strep was a coincidence. I've checked several resources and none of them are saying that a horse with strangles can give strep to a human. I'll have to do more research, interesting question.
Right now, I'm fighting a severe sore throat/fever. New horse has been snotting and coughing. And she won't co operate to get a shot. (vet said to either give her a FULL run of antibiotics or just let it run the course.) A little antibiotics is worse than none.
I'm probably just sick from all the 'romps' in the frigid air with Twister. LOL.