In the song dubbed “the millennial anthem” by the Atlantic, two 20-something friends sing,

Wish we could turn back time to the good old days

when our mama sang us to sleep

but now we’re stressed out.

That’s “Stressed Out,” the top 10 hit from the duo Twenty One Pilots, a couple of dudes who, in the video for the song, like to ride tricycles, sip from juice pouches and hang out in their boyhood bedrooms.

It’s a succinct introduction to the burdens of Generation Why — as in “Why Everything Gotta Be So Hard?”

Millennials are taking bereavement leave from work to build therapeutic treehouses, they’re bringing Mommy and Daddy to interviews, they’re bringing a snack to (and busting it out in the middle of) business meetings, they have a constant need to be entertained and all of them think that they’re shiny unicorns on top of a flowery lawn.

Almost all of the complaints the olds have about millennials (those born between about 1981 and 1996) have a common denominator: This is the generation that just can’t let go of childhood.

Like children, millennials are natural narcissists; research has found they’re a generation characterized by “having an inflated view of oneself” with thin skins and a tendency to whine if they aren’t lavishly praised (“Younger employees are often very resistant to anything that doesn’t involve praise and rewards”). They have short attention spans and announce the need to let their “inner 5-year-olds” out to play.

Departing the plush, comfy environs of childhood is not easy or fun, which is why it’s best done with one harsh, sudden gesture as cruel as that first kindergarten no-look-back drop-off.

At 17 or 18, members of the greatest generation and the baby boomers were handed a union card, or a rifle. Generation X? A latchkey, then a dreary joint-custody plan.

All of these generations strove to extricate themselves from their moms and dads — who, being unaware that “parent” would ever turn into a verb, were happy to let the little ones go.

Baby boomers thought their parents were squares who didn’t understand rock and sex before marriage. Gen Xers, wounded by the baby boomers’ divorces, said (as Douglas Coupland did in his 1991 novel “Generation X”) “Eat Your Parents.”

Millennials never had their dreams shattered. Their parents not only didn’t split up, they’re in the next room, available to provide loans, job contacts and juice boxes on demand.

In the movie “Metropolitan,” released a few months before Coupland’s novel in 1990, the film’s protagonist, Tom Townsend, a child of divorce rapidly distancing himself from his early hardships, is walking by an apartment building when his new friend Nick spots a box of abandoned toys sitting woefully on the street and says, “The childhood of our whole generation is represented here, and they’re just throwing it out.” Tom realizes to his horror that this isn’t just his generation’s toys — they’re his actual toys, because this is where his estranged father lives, and he carelessly dumped them on the curb.

In the 1994 Gen X film “Reality Bites,” when Winona Ryder’s Lelaina says, “I just don’t understand why things just can’t go back to normal at the end of the half hour like on ‘The Brady Bunch,’ ” Ethan Hawke’s Troy Dyer replies, in a lament for all that is heartbreaking, “Because Mr. Brady died of AIDS.”

Millennials never had their dreams shattered. Their parents not only didn’t split up, they’re in the next room, available to provide loans, job contacts and juice boxes on demand.

Today’s young adults expect the lullabies to continue indefinitely, to be carried on their parents’ health insurance until early middle age and for every job to be entertaining, inspiring, creativity-turbocharged and world-changing. No 25-year-old wants to be a tax accountant anymore, because that’s not a job that a kid dreams of. What a kid wants out of a job is not that it be secure but that it be fun.

As Twenty One Pilots sing, “Out of student loans and treehouse homes we all would take the latter.” (What is it with treehouses, millennials?) The duo goes on, wistfully,

We would build a rocket ship and then we’d fly it far away.

Used to dream of outer space but now they’re laughing at our face

Saying “Wake up, you need to make money.”

There’s your proof: Millennials actually need to be told they need to make money. Moreover, this information causes them stress rather than liberation in the challenge of striking out on their own.

Zeke and Hannah need to learn that the rules of existence didn’t reboot themselves when they turned 18. Learning to unicycle is not going to pay the bills. And someday there won’t be anyone there to wash your cereal bowl for you.