Your heart races. You take a deep breath, apologize to those within earshot and talk yourself into taking the next step – the step onto the airplane with your toddler and your infant in arms.

Flying with young children can make or break even the most determined of parents and the most understanding of fellow travelers.

Before your spring break or summer vacation flight this year, consider these tips from the owner of a local travel agency, as well as a mom who has logged many miles in the air with her toddler son.

Determined that her son would grow up knowing his paternal grandparents in Canada, Anna McIldoon took her tyke on his first international flight at 3 months old. Since then, the now 15-month-old has made the trip every couple of months.

Her top three tips come from the voice of experience and are interrelated:

1. Be flexible

2. Be prepared

3. Expect the unexpected

When her son was still an infant, their scheduled flight was canceled, and the duo endured an unexpected six-hour delay. Her rations of food, formula and diapers were put to the test.

As her son slept peacefully on a blanket on the floor of Hartsfield-Jackson International Airport, McIldoon breathed a sigh of relief. Her overpacking paid off.

Since then, she always takes more than she thinks she will need for any flight.

Those traveling with infants and toddlers are allowed to carry formula, breast milk and juice through the airport security checkpoint, according to TSA's website.

Still, it's always a good idea, especially for parents of young children, to pick up a bottle or two of water and some snacks at an airport sundry shop after going through security, said Debbie Ruch, owner of Ruch Travel.

Or you can carry an empty water bottle through security and fill it when you reach your gate.

Sometimes snacks and drinks aren't served on a flight. Again, it's better to have food and drink in your carry-on bag than to have a child crying from hunger or thirst.

As her son has matured into an active toddler, McIldoon says her carry-on bag is now laden with crackers, books and small toys.

"The goal," she said, "is to keep him happy so that the other passengers on the plane can be happy."

Still, happiness is all in one's perspective. On one flight, McIldoon's elderly seatmate watched the toddler gobbling his cheese crackers. Within minutes, the man asked if he could have a few. The two

— separated by more than 70 years but only a few inches of personal space — bonded over crackers.

On another flight, the youngster waved his sippy cup proudly in the air. The top flew off and bathed their seatmate, who was wearing a suit, in milk.

The man smiled, wiped off his suit and said he was on his way home to see his five children.

"Oh, that's another tip: Keep your sense of humor," McIldoon said.

As children become old enough to voice opinions, Ruch said, you should involve them in the packing process.

Children who pack their own snacks, toys or electronics in their own carry-on bags have little room for whining, she explained.

However, she added, parents need to know what their children are packing so there are no surprises going through airport security.

Try to keep surprises for children to a minimum also, she advised.

"Prepare a toddler or young child for what to expect before flying, such as going through a security line at the airport, having one seat to sit in on the airplane and so forth."

"Early" is another tip of travel agent Ruch.

"Book early and board early," she said.

If a flight is booked early enough, there's more of a chance that parent and child can sit together, easing the fears of not only parent and child but also those of unsuspecting passengers.

Also, she said, those traveling with young children are often allowed to board the aircraft before other passengers.

"Take that opportunity!" she said. The extra time should allow parent and child to get settled, and will give the child a chance to "check everything out," she said, such as seatbelts, window shades and even the lavatory.

"Make it fun," she said. "Explore everything."

Parents may also want to check out the changing table in the lavatory, McIldoon said.

"A baby's got to go when a baby's got to go," she laughed.

To make getting to the gate easier, parents can check strollers or car seats at the gate without having to pay a baggage fee. Put the stroller or car seat in some kind of protective cover, even it's only a heavy-duty garbage bag, before checking it, Ruch said.

To avoid extra scrutiny or delays, Ruch advises that parents travel with documents, such as a child's birth certificate and/or a certified letter of consent, granting approval for the child to travel with one parent, signed by the parent who is not traveling with the child.

Travelers may not always need these documents, but it's better to have them, just in case they are requested by airport officials, she said.

Children flying domestically with a parent are not required to have a photo ID, according to the FAQ section of TSA's website, but those flying internationally need a passport.

Whenever McIldoon is traveling with her son but without her husband, she never leaves home without the letter of consent.

"Although it's rare for a child to get lost," having some form of identification on a young child can be helpful if parent and child become separated, Ruch said.

Finally, just as parents get the hang of traveling with young children, the day may come when children may need to travel without a parent.

Airlines differ on when children are permitted to travel as unaccompanied minors, and there are often extra fees involved, according to a U.S. Department of Transportation website, so be sure and know your particular airline's policies, Ruchs said.