On Christmas Eve, as my wife, Amy, and I got ready for the next morning, Amy said she had one last present for our two kids: a $100 bill stuffed into each of their stockings. I balked.

I understood why she might want to give the money to our 9-1/2-year-old son. We didn't buy many of the items on his oh-so-long wish list; the cash would allow him to purchase those things that were most important to him.

"But why," I asked Amy, "would you feel compelled to give a $100 bill to a 2-1/2 year-old?" It wasn't that the gift was extravagant— though it certainly was. It was that the gesture was entirely meaningless. Our little girl doesn't know a greenback from the green construction paper she scribbles on.

"You have to be equal," Amy insisted. "My parents have always been equal with what they've given me and my brother, and we have to be equal with what we give our kids."

Though I completely disagreed, Amy was steadfast, and so each of our kids found Ben Franklin hiding in their stockings Christmas morning.

My daughter, as expected, couldn't have cared less.

I've been thinking about that episode for several weeks now, wondering just how far the notion of equality should extend within a family. Just because kids are equal in your heart, does that mean they must also be equal in your wallet?

As I see it, there are two broad issues at play. First, there's making equal the amount of money you save or invest for each child for college or for whatever reason the kids ultimately want to use it. And then there's the situation like we faced at Christmas, when you aim to make equal the discretionary expenses for gifts—or, maybe, for vacations the kids take with friends and family, or extracurricular activities they pursue.

For months, Amy has been riding me to open a college-savings plan for our daughter. I haven't felt much of a rush to do so because we're saving for our son, and after our daughter arrived I increased the amount of savings going into that account. At some point, I figure, we can split that account in half and give that portion to her-and, voila, equality.

In truth, that's lame on my part. When our son goes to college, he could end up consuming the entire account for whatever reason. That would leave our daughter reliant on loans and grants or force her to consider a lesser-quality school. In the end, that's just not fair to her. So, conceding that Amy's correct, I'm opening a separate account for our daughter to make things equal for their college funding.

That's a relatively easy decision to make; both kids deserve the same opportunities in life. But that logic disappears when you apply it to equalizing discretionary spending for the sake of not playing favorites. My daughter has no appreciation of the comparative value of what she and her brother receive—only that she does receive gifts, too. Call it the equality of volume, not value.

To a certain degree, age plays a role in this. Our son is at an age where his material wants are substantively different than our daughter's.

He wants an iPod, a motor scooter, a digital camera, video-games—all pretty pricey stuff. Our daughter is happy with the doll I won at a church fair, or the crayons that cost a dollar a box.

Here's the problem I have with Amy's approach: If we drop $350 on a video iPod for our son, then our daughter stands to get $350 of dolls and crayons. Sure, that's an extreme example, but it's the logical extension of Amy's argument. As she told me when I questioned her for this column, "If I spend $300 on one child, then I try to balance that out by spending roughly $300 on the other child."

To be sure, with kids closer in age, the demands of equality can be tougher to navigate. My New Orleans friends, Drew and Colleen, have a boy and a girl very close in age and, Colleen says, when the kids were younger "we gave them the same number of things, though not necessarily a monetary equality." Now that the kids are older and understand value, Drew says, "we find ourselves in the situation often where we give one child something and are forced to give the other a matching gift."

But whatever the age, to me this is all blind mathematics. It implies that the gift is all about its nominal value—the equality of cost—not the psychic value of what the gift might represent. It doesn't take into account that for one child, the perfect gift might cost $100, but for a sibling the price tag is $200. It assumes that kids don't care what they get, as long as the price is right.

I don't believe that the monetary difference really matters when both kids ultimately receive what they want. If Child No. 1 desperately wants a $300 camera and Child No. 2 is crazy for a $200 scooter, Child No. 2 isn't going to be happy with a S300 videogame system simply because it's the same price as the camera.

My problem, according to Amy, is that I am an only child and "this is a sibling thing you can't understand."

Kids, Amy insists, want equality. "I always watched to see what my brother received to make sure it was equal with what I got," she told me, adding that our son was keeping tabs at Christmas on what he and his sister pulled from the stocking. "I don't want him to think he gets more than his sister. And while our daughter might not understand the equality yet, when she's older she'll be looking to see the same thing."

That may be true, although perhaps that's because of the lessons we're teaching them. And even if our kids do look at it that way, that doesn't necessarily mean that we— parents—must define equality by our kids' expectations, or by whatever strategy our parents employed to show that they didn't play favorites.

The solution seems obvious: If our son questions why the value of his gift is greater than his sister's, explain to him that at her age she doesn't have the same need for money that he does, but that when she reaches the age he's at now she'll receive equivalent gifts. Then, when our daughter is old enough to question why her older brother gets more, we'll explain to her that as her wants grow in value she'll be receiving more, too, just as it was with her brother.

As I see it, it's not unlike an allowance: A younger child starts off with a smaller amount and grows into larger sums with age.

Amy still disagrees, and so our debate continues. As she says, "You give them equal amounts, or you give them each nothing."

*****

By Jeff D. Opdyke, for The Wall Street Journal Sunday, February 19, 2006