People used to get happier as they aged. That might be changing — now, apparently, we’re raising a generation of soon-to-be-disappointed young adults.

That seems to be the message from a new report in the journal Social Psychological and Personality Science. Jean Twenge of San Diego State University, Ryan Sherman of Florida Atlantic University and Sonja Lyubomirsky of UC Riverside write, “increasingly unrealistic expectations for educational attainment, jobs, material goods, and relationships may feel good for adolescents but be disappointing for mature adults who cannot attain these goals.”

In other words, the combination of modern coddling parenting styles — telling kids they can have everything and be anything — combined with the difficulties of our current world make for a very rough transition into adulthood.

It’s not only that the economy is still in the dumps, making it hard for young adults to get good jobs and see their wages rise. It’s also that marriage rates are low and that people are waiting longer to tie the knot.

Moreover, we’re seeing a decline in other things traditionally associated with how happy people say they are.

People tell researchers they have fewer close friends, they’re more likely to live alone and have fewer communal (including religious) ties.

The question is: How do we prepare kids for the world ahead of them so that they don’t experience such disappointment when they grow up? Do we just set expectations low? That’s unlikely to catch on among the ever-optimistic American populace.

Many middle- and upper-class parents say they worry about raising kids “in a bubble.” Their kids live in neighborhoods and attend schools that are safe, insulated from poverty and drugs and filled with other families who look like them and share their values.

Some of them take a different approach — sending kids to schools in other neighborhoods, taking them to volunteer at local soup kitchens. There’s nothing wrong with such strategies, of course, but hours of community service is unlikely to make kids’ expectations for adulthood any more realistic.

The likelihood is that they’ll still exist in a bubble. Take the college students this past week, who have been protesting various micro-aggressions. They’ve been raised in families that talk about injustice in the world all the time.

But rather than finding themselves prepared for what the world has to offer, they’ve withered in the face of Halloween costumes. They shut down a university because a guy driving off-campus yelled an ethnic slur at someone. They’ve demanded resignations because administrators have suggested that free speech may be more important than hurt feelings.

What could the parents of these delicate flowers have done differently? For one thing, they could have taught them some basic truths about human nature — truths that are the same across lines of race, class and gender.

First — here’s a shocker — the world is filled with people who don’t care about your feelings. And if someone insults you, you can either defend yourself or you can ignore it. But running to an authority — parents, teachers or administrators — only cements your reputation as a whiny jerk.

Or what about this? The world is filled with people who need to make a living. And you will likely be among them some day. So even if you’re insulted by someone or find some policy or bit of decor in your office objectionable, you’ll be expected to continue doing your job.

Again, complaining to authority figures about every slight is not a recipe for success. And it’s certainly not going to get you a paycheck.

Finally, good intentions don’t change the world. No matter where you go to school or what kind of profession you go into, there are things you’ll want to change. There’s nothing wrong with that. But bringing a campus or a business to a grinding halt just so that you can hold up a self-righteous sign isn’t the way to effect change.

Big change requires hard work, sometimes through the political institutions that seem old and stodgy. And sometimes change requires the use of force. People who murder innocents at nightclubs and stadiums care not a whit about your feelings or whether Americans mean well.

And if your parents forgot to mention that along the way, adulthood is going to be a real letdown.

Naomi Schaefer Riley is a senior fellow at the Independent Women’s Forum.