Sealy,
In considering advice, there are alot of unkowns to your question. Where you are, what kind of grass, what kind of fence, etc. Each of those would change the advice that most would give about what kind of cattle and how many and what age. However, a good, general thought for your situation would be to get 2-4 beef cross calves that have been fed on the bottle and are weaned----around 8-12 weeks old. These will be much gentler and easier to work with. Also, as beef crosses, they will make good eating beef. This young, they will be easy for your children to work with and enjoy. But, weaned, they will only need some grain each day and your pasture to grow and thrive. There are generally local farmers who raise calves on the bottle and sell them after they are weaned. To me, that would be better for you instead of going to a sale barn when you are not experienced at that. Also, your invetment will be considerably less than if you buy 500 lb weaned beef calves that might be wild. I do not know about your horses, but some horses chase and kick cattle, so that is something you will need to find out is how they act around calves. I am sure there will be many other thoughts from the board, but this is a good general way of doing it.