NEW YORK—It’s a few minutes to showtime. The guests are all seated, the musicians are warming up.

Behind the scenes is a frenzy. The groom is nervous, his face as white as his new shirt. A bridesmaid searches for her misplaced camera. Ties are straightened, makeup checked. Suddenly, it’s time to line up.

The grownups are busy doing the things grownups do right before a wedding. Young children, though, are more than likely doing the things they do pretty much all the time: playing, coloring, being anywhere besides where they’re supposed to be RIGHT NOW.

So how do you get those pretty little flower girls with ringlets and pouffy dresses and the handsome tuxedoed ring-bearing chaps to take that matrimonial walk at the appointed minute, when you can’t even get them to eat over the table or remember to say please and thank you?

Preparation, practice and a plan (better throw in a backup plan, too) will go a long way to getting young attendants down the aisle with smiles on their faces and heads held high.

Weddings, it should be remembered, are adult affairs that roll right through naptime or beyond bedtime. All those big people. All those flashing cameras. All those hours away from a kid’s routine.

“This is so unlike anything they would have ever been asked to do,” says New York child psychologist Laurie Zelinger. “They’re playing in our ballpark now.”

She recommends explaining to these youngest members of the bridal party, typically between ages 3 and 7, that they have an important job. That way, when everybody oohs and aahs, they are less likely to feel self-conscious and more likely to focus on what they’re doing.

To help avoid the flower girl who walks down the aisle sucking her thumb or crying, or the ring bearer who dances or practices his karate moves, teach them exactly what they’re supposed to do, Zelinger says.

Read books together about weddings. Let them watch a wedding video to see a ceremony. Look at family wedding photos. Get them familiar with the clothes they’ll be wearing.

Practice at home with a flower basket and silk petals or a mock ring pillow.

“As they practice and get better at their duty, they will build pride in their role as flower girl or ring bearer and want to show off” on the big day, says Nicole D’Ambra, a wedding consultant in Los Gatos, Calif.