I am a beginning aquarist, so please understand I'm no expert. However, everything I have read has told me that goldfish require 10 gallons each. The reason they hardly ever grow very large or live very long is because people (usually very well-meaning people) don't know how to keep them properly. My roommate has a 37-gallon tank with four goldfish, and that is a very overstocked tank. Her oldest goldie is 3 years old and is about seven inches long, including tail. In perfect conditions, they can live up to 40 years and be over a foot long! Goldfish are great pets, but they're a hard fish to begin the hobby with.
Here's my advice. First, check with your parents to make sure it's okay for you to do anything. If they say it's okay and are willing to help out, get yourself a 20 gallon tank. Craigslist and garage sales are your friend if you don't have a lot of money! You also need substrate, plants (plastic or silk ones are fine) and a filter. In the meantime, read everything you can about goldfish, the nitrogen cycle, filtration, water conditioning, and feeding. You could end up with a fantastic new hobby and some very happy fish.
If you find you've gotten yourself into "deep water", so to speak, and really want to save the fish, you may be able to find a local fish shop, aquarium, or fish enthusiast to adopt them.
I think your hearts are in the right place. I wish you the best of luck.
-Morgan