Others may disagree, but I think the best thing would be for you to go (preferably with your kids!) to the library and get some books on aquariums. They provide a step by step "how to" that a question and answer exchange cannot fulfill.
I hope you will research in this way! Books have been kind of forgotten about, but it shouldn't be so. There are websites we can recommend to you also, for example
http://freshaquarium.about.com - but I think a book would be great for you and your family. Just take it nice and slow and if you have any questions, ask them ahead of doing anything like buying fish or making an equipment purchase. It's a lot harder to help when people ask "I got 3 goldfish, they're in a 10 gallon tank is that ok?" instead of "Can I put 3 goldfish in a 10 gallon tank?" And once someone has already bought a filter, it's hard to say "That's a piece of junk!" but if someone asks for their opinion in comparing a few different kinds...you get what I mean?
To answer your question, it is a 30 gallon tank...and it will take longer to cycle. You should read up on "fishless cycling" (Google it if you haven't heard of it). Instead of making fish be the ammonia source, flake food, a piece of shrimp or pure ammonia will do it.
Go to your local pet store, look at the fish there are for sale. Avoid cichlids or goldfish, but otherwise write down the names of what strikes your fancy and come back here!
Livebearers are great for children, guppies and platies can fit just right in this tank. Balloon belly mollies could too, but they are often not very healthy because of their inherent problems that come with their deformed (on purpose) shape. Avoid swordtails for a 30 gallon.
Questions are great, and of course they will always arise....but the best way to learn is to read, read, read all you can!
