Figure out finances

It's essential to decide who's going to pay for what before you go. Sometimes grandparents treat the entire family as a way to mark a special event, like a birthday or an anniversary. If so, find out what's included. Are they paying for the airfare or just the hotel? What about meals and amusement-park passes? While Bagdade's parents covered lodgings and airfare for their Costa Rica trip, "we paid for certain things along the way, like museum admissions and some meals," she says.

If your folks or in-laws are footing the bill, you might show your appreciation by treating them to at least one thing, like a family dinner or special souvenir.

Know when to go solo

Too much togetherness can make anyone edgy, so make it clear up front that you're not expecting to do everything as a group. That way, your parents won't feel bad going to the movies while you settle in for an evening watching the Disney Channel in your room.

Keep in mind that it can be fun to match up different generations for a few hours. Grandpa may have a great time taking the kids to hunt for seashells on the beach while the rest of you troll the outlet mall. The key is to be flexible.

It's also important to manage your expectations. You may think you'll hire a hotel babysitter one night and eat out somewhere fancy with your in-laws, only to realize your child isn't ready to be left in an unfamiliar place with a stranger. And speaking of babysitting, it's smart to ask your parents in advance exactly how often they're willing to do it. Some are thrilled to have some alone time with their grandchildren; others may balk at your leaving the kids with them for hours.

Finally, don't worry if you run into a little friction. "My mother wanted to take a family photo, and dictated that we all had to wear white shirts. It caused lots of tension. Some of us thought we should be given a few colors to choose from; others thought we should be able to wear whatever we wanted," Barnett says. "In the end, though, we didn't dwell on it. Mom and Dad wore matching outfits, and the rest of us had every variation, including Hawaiian shirts. And it turned out to be a great photo!"

Mary Garner Ganske now takes a three-generation vacation every year.