Does anyone have any suggestions for horse safety and young children? I want my children to be safe and respect the horses, but I don't want them fearful.

The biggest thing is don't show fear yourself. Kids, and horses, can sense fear and will react upon it. Teach them to be quiet around the horse, not to make any sudden movements that may scare the horse. Teach them to stay away from the hind end, and that the front end loves carrots LOL.
Be consistant and teach them to respect the horse. If you teach through example, your kids won't fear them.

You could always start off with introducing them to miniatures. The risks are far less with a smaller horse, but the basics of care are similar (just smaller poops to clean up ;)).

There are many petting farms around that you could take them too.

If the child has not been around horses before, I would start with a movie or reading about horses. Talk to them about the right and wrong ways to approach a horse and about caring for them. This will start familiarizing them with horses which could make it less of a fearful start.

Yes, media exposure will definitely help to reduce the risk of fear around them. But it won't help them deal with the issue of size-horses really can seem gigantic to a little one. It also won't teach them about the smells and sounds of the stables.

The only way you will get through that is exposure to a real stable.

Another idea to try, is to take the kids to a few shows, especially ones with children participating. The experience can serve to spark their interest.