How do you break in a pony?

It's just like breaking a horse. You break a horse, not break it in. This is it's first training when it first learns to be handled or ridden. Usually you should start out slow, at about the age of 3, which is when their knees are fully developed. You start out just by leading them, then fitting them with a bridle and saddle. You can put a little weight on it's back to see how it reacts. Eventually, you start riding it and then training it. Unless you have broken many horses/ponies before, it's best to find a trainer that will break the horse for you.