|it really depends on how much money you want to spend and whether it is important to make that money back.
making the money back is simply a matter of focusing more on the business of photography than actually taking pictures. this means putting together the sales collateral, the website, etc. and putting the word out that you are available to shoot. you also need to come up with reasonable rates that reflect the value of what you are offering. there a plenty of parents out there with great gear that shoot every event their kid is at and then give all the other parents great photos for free. believe me, it's really hard to compete with free.
however, if you can do something the other parents can't do, then you have an opportunity. this is especially true if you have great post-processing skills and can make posters, collages, books, etc.
as to the gear, that is really a matter of what it takes to get the job done. two bodies are great for sports, allowing you to shoot both ends of a court or field without having to change lenses. all the same, it's not as important as having an understand of the sport you are shooting. if you know what you are looking, you can use your long lens to get that stuff and then switch to another lens for other stuff. if you are shooting a single kid, you don't need 500 pics. even if you are shooting for a handful of parents, you don't have to overshoot in order to get the handful that you need to present.
in my experience, it's better to push the gear you have as far as it will go until you honestly know what's holding you back. is it low-light? then you need either faster glass or a sensor that handles higher ISO. is it focusing? maybe you need a body with better auto-focus. is it more you than the camera? maybe you might just need more practice.
this can be fun, rewarding, and lucrative - but, it does take a lot of work.