If I hear “That’s not fair” one more time from my son (who’s 9), I will scream.

Fair: the four-letter word kids are most obsessed with. They expect — no, they demand — that parents be 100% equitable, at all times, in all places, with all children. Even if we could accomplish this impossibility, we still would not get credit for it. Kids define fair very personally. To Justice, fair means getting disciplined equal to or less than his sister, Mercy, even though to be truly just you would have to discipline him three times as much because he earns it. As it is, you let some misbehavior slide so as not to appear grossly biased.

“You’re not fair” comes in limitless guises: “You like Robin better because she’s your pet.” “I’m nothing but a slave around here.” “How’d you run the house before I was born?” “How come you never send Jolie to her room?” “I’m going to treat my kids a lot better than you treat me.”

All such commentary on your parenting wraps around one theme: You simply are not acting with equity, as seen through juvenile eyes. Indeed, I hope not. Children are not exactly impartial judges of what is correct conduct, particularly where they’re involved. Put another way: If Holmes always considered you fair, that would be a sure sign you’re not.

Loving parents strive to be fair. You work at meting out time, attention, even material goodies in roughly comparable amounts. But because no two children are identical — even identical twins — no two parenting tracks are identical. Butkus cleans his room anytime the sun comes up. Hazel won’t touch hers unless you threaten to ground her until she owns her own home. Because of their distinct temperaments and personalities, children require very different approaches. They don’t recognize this, so they sometimes interpret your legitimately dissimilar treatment of them as playing favorites or changing the rules in the middle of the game.

Another reality breeds the inequity charge: age. “Why do I have to go to bed now when Eve (older sister) gets to stay up later?” “When I don’t pick up my toys, I lose them for a week. Murdock (four years younger) only loses his for three days.”

Childhood is defined by ever-changing privileges and responsibilities. Ten-year-old Wendell enjoys greater freedom than his 6-year-old sister. That’s as it should be, he says. But at the same time, he chafes under your increased expectations. Neither Wendell nor his sister sees the whole picture. If they did, you wouldn’t get nearly the same amount of complaints.

How can you mute the unfairness accusation? You’ll never completely silence it. Even adults are quick to cry foul when we don’t feel life is treating us fairly. My first suggestion is to stop explaining yourself each and every time you hear “That’s not fair.” In trying to talk a child into a grown-up’s view of justice, the more you explain, the more behind you get.

A standard parental comeback is “Life’s not fair.” This is true, but kids don’t buy it. At the moment of discipline, it’s wise to live by: the less said, the better. Explanations, if needed, are best reserved for later.

As your son gets older, you might consider something like: “Justice, you really seem to be caught up in everything being perfectly fair. So, from now on, when you complain, you’ll write a 200-word essay on fairness. This will help you better understand what you’re talking about.”

The doctor is always