First off, do you need a passport? If you are traveling internationally by air regardless of age, each person must have their own passport. If you have NEVER had a passport, you'll need to apply in person. If you are renewing, you may qualify to renew your passport by mail. The web site below will be able to help answer that question for you.
If you are traveling by sea (cruise ship), the rules are a little different. There is something called a "Closed-Loop" cruise and here are the regulations for that: If you are a U.S. citizen, and you board a cruise ship at a U.S. port, travel only within the Western Hemisphere, and return to the same U.S. port on the same ship, you may present government-issued photo identification, along with proof of citizenship (an original or certified copy of your birth certificate, a Consular report of Birth Abroad, or a Certificate of Naturalization). Please be aware that you may still be required to present a passport to enter the foreign countries your cruise ship is visiting. Check with your cruise line to ensure you have the appropriate documents.
Traveling by land internationally, you may use a passport book or passport card. Determine what you need at the below web site, but basically, if you are going to spend the money on a passport, go ahead and get the book. If you then had an emergency, you would be able to fly if need be.
Getting your passport...
Go to http://travel.state.gov/content/passports/english.html. On the right hand side of the page, you will see a box with links to forms. Download the appropriate one and fill out on your computer, print and take with you so you do not have to do that while you are at the facility. Gather the appropriate documents that will go with your paperwork:
<li>Proof of citizenship - your original birth certificate with the raised seal. Unaltered and undamaged. They will return it to you when your passport is issued (keep a copy of it at home in your files.</li>
<li>Proof of identity - your driver's license will work just fine. Make a copy of it front and back to put with your passport application.</li>
<li>Picture - they are PARTICULAR about the picture! It must be color, 2 X 2 and show full frontal face. I highly recommend that you pay to let them make the photo at the facility where you are submitting.</li>
<li>Fees - The current rate (subject to change) is $110 for an adult first time passport book. A separate check or payment of $25 is for processing. The web site will break everything down. The fee for pictures will vary from place to place, but typically is around $15.</li>
The web site offers a search engine to help assist you in finding a local facility that processes passport applications, but most U. S. Post Offices will do it. Call or ask the next time you are by one of them. Some have set times and days that they accept them while others require an appointment. If you have all of your paperwork in order, your process will go smoothly. If you know well in advance that you'll be traveling overseas with the family, you'll have time to budget the passports...do one a month so that the fees aren't such a chunk at one time. Routine processing time is 4-6 weeks.
Good luck and safe travels!