02/12/2012 09:29 am ET | Updated Apr 13, 2012

Ask Airfarewatchdog: Lap Babies, Pets On Planes, Miles For Investments answers your questions about air travel. We answer as many as we can in this column or by email to

Q: I plan to travel with my 16-month-old twins. Do they need a reservation? How do I make sure they can fly with me when I reserve a ticket for my husband and myself?

A: If traveling domestically, your infants, because they're under two years old, do not need to buy a separate fare and you don't need to inform your airline beforehand that they'll be traveling with you. They can be considered lap children, which means they must sit in your laps for the entire flight. While this is "legal," you should consider that modern jetliners take off and land at high speeds (100 miles per hour or more) -- and they can decelerate just as quickly.

You wouldn't put a baby in your lap while driving your own car, even if traveling just 15 or 20 miles per hour (in fact, it's illegal); you'd put them in a car seat. So I really don't recommend seating your children in a speeding jet airplane in any other way. If the plane stops suddenly, your child will become a projectile, and infants have indeed been injured in such circumstances, and also during extreme turbulence. Also, it's incredibly uncomfortable having a baby in your lap on a long flight.

Keep in mind that if you're traveling internationally, you're supposed to pay 10 percent of the applicable adult fare, and your infants will need to buy their own fare, even if they're sitting in your lap, so you'll need to inform your airline that they'll be flying with you when you buy your own fare.

Q: If traveling with a small pet under the seat in a pet container, are there any charges for the pet and, if not, are the pet and its container considered your carry on or are you allowed one carry on along with the pet?

A: Airlines do indeed charge a fee for pets carried in the cabin, and the fee varies between airlines. United Airlines, for example, charges $125 each way. Southwest charges $75 each way. You can easily find the fee for your airline by web-searching "[airline] + pet fee." Airlines limit the number of pets per cabin, so you should reserve a spot for your buddy by phone at the same time you book your flight.

Make sure that your pet's container is small enough to fit in the seat in front of you (and that you don't book a bulk head seat, which won't have under seat storage). And unfortunately, your pet's container does count as your one carry-on piece. The above information applies to domestic U.S. flights; fees and regulations may vary for international travel so check with your airline before booking your trip, and these fees and policies are subject change without notice.

Q: I read that I could get 50,000 frequent flyer miles for opening a new Fidelity Investments account of $100,000, but I cannot find that deal mentioned anywhere online. Do other banks have similar deals?

A: United, American and Delta Airlines offer up to 50,000 frequent flyer miles when you open and fund a non-retirement account at Fidelity Investments of $100,000 or more; or 25,000 miles for an account worth $50,000 or more; or 15,000 miles for an account worth $25,000 or more. US Airways offers up to 25,000 miles for investing $50,000 or more in a TD Ameritrade brokerage account. To find links to these offers, simply web-search "[airline] + Fidelity Investments" or "US Airways Dividend Miles + TD Ameritrade."