You’ve probably heard jokes about the oldest child being a mini-adult while the youngest is the eternal troublemaker. It turns out there’s some science behind those jokes. A 2017 study from MIT and Northwestern University found that second-born sons—specifically boys—are 20–40% more likely to face disciplinary issues than their older brothers. In Denmark, second sons were 40% more likely to end up in prison by age 21, while in Florida, school suspensions were up to 72% higher for them. These numbers aren’t random: they show up across countries, regardless of family income or cultural background.

But why second-borns? And why boys in particular? Let’s break it down step by step—with psychology, examples, and explanations anyone can understand.

1. Parental Attention: The First Child Is an Experiment, the Second Is “We’ve Got This”

When the firstborn arrives, parents are in full “battle mode.” Every coo is documented, every fall is a tragedy. Psychologists call this hyper-parenting in the early years. Parents set strict rules, monitor constantly, and devour parenting books. The child grows up in a structured environment where every action has consequences.

Then the second child comes along. The parents are now “pros.” They’re less anxious, less nitpicky. Studies show that parents spend 20–25% less time on direct interaction with the second child (reading, playing, talking). It’s not that they’re loved less—it’s just that the older sibling already demands attention, and parents spread themselves thinner.

Psychological explanation: Less structure = more room for experimentation. The second child quickly learns that rules can be “tested.” If the older brother got scolded for climbing the cabinet, the younger one thinks: “What if I do it quietly?”

2. Risk and Independence: Second Sons as “Boundary Explorers”

Psychologist Frank Sulloway, author of the birth order theory, explained back in the 1990s that each child carves out a “niche” in the family to avoid competition. The firstborn takes the “responsible leader” role. The second son sees that niche is taken and chooses the opposite—rebel, explorer, risk-taker.

This isn’t a conscious choice. It’s an evolutionary strategy. In nature, younger offspring often take more risks to find their own territory. In families, it’s the same: second sons are more likely to:

• ignore rules (“My older brother already tried that, I’ll try it my way”);
• seek attention through provocation (because calm behavior doesn’t earn “bonuses”);
• copy peers rather than parents.

Fun psychology fact: Second sons are more likely to become comedians, extreme athletes, or entrepreneurs. Famous “second sons” include Stephen Colbert and Justin Timberlake. Risk is their superpower—but in childhood, it often backfires.

3. Role Models: From Parents to Older Siblings and Friends

Firstborns look to parents. Second-borns look to older siblings. But here’s the catch: older siblings are already “testing” the rules themselves and often model informal behavior. The younger brother sees: “Big bro played video games until midnight—and nothing happened, he’s fine.” Or: “He argued with Mom and Dad—and got more freedom.”

Research from Florida showed second sons are 37% more likely to hang out with “troubled” peers. Why? Their social world is broader. Firstborns tend to stay “within the family circle,” while second-borns seek friends outside the home.

Psychological explanation: This is called social learning through observation (per Albert Bandura’s theory). A child copies not the person who behaves “correctly,” but the one who gets rewarded. If the older brother got attention through mischief, the younger one will repeat it.

4. The Gender Factor: Why Boys Specifically?

Girls can be second-borns too, but the stats are milder for them. Why?

• Social expectations. Boys are historically encouraged to take risks (“be a man”), while girls are often encouraged to stay calm (“be ladylike”).
• Emotional regulation. Girls, on average, tend to develop brain areas for empathy and self-control earlier (per neuropsychology data).
• Parental oversight. Second daughters are more likely to stay “under supervision”—they’re less often let loose “on the street.”

So the “second son” effect is a combination of reduced oversight, a drive to take risks, and gender stereotypes.

5. What Can Parents Do? Psychological Strategies That Work

The MIT researchers offer three simple but effective tips:

1. Dedicated one-on-one attention. The quantity of *focused* time matters. 15 minutes alone with each child daily already reduces the behavior gap.
2. Clear boundaries for everyone. If the older kid can’t use the phone after 9 PM, neither can the younger one. Consistent rules = less temptation to break them.
3. Positive rivalry. Encourage brothers to help each other, not compete. For example: “Whoever comes up with the most creative way to clean the room gets a prize.”

Conclusion: Second Sons Aren’t “Bad,” They’re Just Different

They’re not born troublemakers. They’re born into a family where there’s already a “main character,” so they pick their own role—explorer, rebel, comedian. Birth order psychology shows: we’re not victims of circumstance, but circumstances shape us more than we think.

So if you have two sons—don’t panic. Give the younger one structure, attention, and clear boundaries. And maybe he won’t become the “problem child,” but a world-changer who does things his own way.

Sources and Observations:

• MIT/Northwestern Study (2017): “Birth Order and Delinquency: Evidence from Denmark and Florida” — published in The Journal of Labor Economics. Authors: Joseph Doyle, Sanni Breining, David Figlio, et al.
• Sulloway’s Theory: Frank J. Sulloway, Born to Rebel: Birth Order, Family Dynamics, and Creative Lives (1996).
• Practical Observations: Child psychologists (e.g., from Happiest Baby) note that the effect weakens in families with high involvement from both parents.

This isn’t a verdict—it’s an explanation. And a chance to raise both kids happy. Just in their own way.