This time they’re arguing about a deck of cards, Crazy Eights, a Christmas gift, suddenly my granddaughter’s favorite Christmas gift, a deck now missing one 4, one 6, and two 9s. How did this happen?

“I left them right here, Mimi, on my bed in this closed box,’’ says Megan, “and he opened it and threw the cards all over the room, and now the deck is ruined.’’

All 59 pounds of my 9-year-old granddaughter stomp down the hall and into the bathroom in tears.

Her 7-year-old brother stands still as wood trying to feign innocence but his big eyes cannot lie. “Why, Luke?’’ I ask, but it’s like asking the sky why it’s blue or a fish why it swims. “Please help me find the missing cards,’’ I say, shouting down the hall that the cards have not disappeared, that they are in the house and that they will be found.

And what do you know? Luke finds them and with a much-practiced apology presents them to his sister, who counts them and then returns them to the sacrosanct, once-again-closed box.

And blessed be God, for a few minutes peace reigns.

Until they start arguing again, this time about a long, blue silky ribbon, which wrapped up Megan’s birthday present. “Give it back, Luke!’’ she yells, the ribbon, I swear, a bigger hit than the pricey gift it adorned. She has clutched it, swirled it, and wrapped it around herself for days. It has been constantly attached to her. But now, he insists, he “found’’ it.

“You know it’s hers,’’ I reason.

“Yes, but . . . ’’ he says.

That’s what they say. That’s how children argue. “Yes, but.’’ “It’s not fair.’’ And “It’s my turn.’’

“It’s not fair, Mimi. Luke got to choose the episode of ‘Sophia’ yesterday.’’

“Yes, but Megan chose two before that!’’

“Because you were somewhere playing, Luke. You weren’t even in the room.’’

“You know it’s my turn, Megan. You know it is.’’

Then they glare at each other.

You would think they were enemies. But the truth is, they are not.

The first night they were here, two little kids away from home, at their grandparents’, yes, but not in their own beds with their parents right down the hall, they united. All at once, in a split second, all arguments were forgotten and there they were not combatants anymore but compatriots, looking out for one another.

I tucked them into their beds, in their room with their favorite stuffed animals, pressed repeat on the CD player so that John Denver would sing “Country Roads’’ over and over, which Luke likes, told them all the fun things we were going to do the next day, and kissed them good night.

Then Luke said, “I miss Daddy,’’ and began to cry.

And Megan, who had spent half the day annoyed with him, sat up and said instantly, “It’s OK, Luke. Come sleep in my bed. You’ll feel better.’’ And he crawled in and she put her arm around him and he closed his eyes. And that’s how they slept. And that’s how they have slept every night since.

Because that’s the way it is with kids. Opponents one moment. Allies the next. That’s the way it is with families, too. Fists clench in anger, but then arms open, and all is right again.

In the days immediately after Sept. 11, 2001, dark days, dark times, we knew that this nation is family, one nation, all of us standing arm in arm at vigils, in prayer, comforting each other, knowing that all of our differences combined could never add up to all that we have in common.

I listen to my grandchildren argue. And then I watch them sleep. And I wish for my country only this: That we remember what unites us, all we share, and who we were when we were frightened like children in the night.

One family. One nation. One.

Beverly Beckham’s column appears every two weeks. She can be reached at bevbeckham@gmail.com.