Entering adulthood used to be like wading into a gently sloping lake. You got your feet wet with a degree or job. Then maybe you found an apartment, and eventually a life partner. Soon, you were swimming in deep water.

But today, it feels as though the water gets deep fast. Young people can’t just splash around and “find themselves” anymore. The world has changed.

Work can disappear with little warning. Skills grow obsolete fast. Lifetime employment and corporate loyalty are mostly things of the past. Compared to two decades ago, the average American worker puts in an extra 164 hours per year on the job, according to economist Juliet Schor. And adjusted for inflation, middle-class U.S. workers make less than they did in 1971.

These pressures mean that anyone who wants to “have it all “ — career, family and leisure — needs to look way ahead. We parents would be wise to talk through the choices very explicitly with our children, especially the majority who are likely to want both work and kids.

We can explain the need for a sharply different perspective on career planning. For example, a friend of mine in her 20s who just got married says that she and others her age won’t rely on working for an employer. The long hours and lack of security aren’t worth it. Her plan is to run her own business and live frugally. Great idea; I hope for her sake it works out.

Another option is to choose an explicitly family friendly career, something women have been doing for ages — a career with predictable hours and even some job security. Men increasingly are doing likewise; they make up ever more of our nurses, schoolteachers, bank tellers and food servers.

Even for the most ambitious, there are ways to craft a career that allows for more family time. A study of nearly 1,000 women who graduated from Harvard College between 1988 and 1991 showed that, 15 years after graduation, the ones who became doctors and lawyers had an easier time combining work and family than did those who later got an MBA. The doctors and lawyers had shifted to part-time work, opened their own practices with like-minded colleagues, or moved into the nonprofit sector or government work. The businesswomen, by contrast, faced an either-or choice: Put in grueling hours or quit.

Marissa Mayer, the new Yahoo chief executive, is an example. She’s 37, will give birth this fall, and plans “a few weeks” of maternity leave during which she will continue to work. But if you want a different sort of work-family balance, then perhaps you shouldn’t plan on following in her footsteps.

Stories about families working together to make hard choices are encouraging. Austrian tennis player Sybille Bammer, for example, had a child at 21 and quit competing. She went back to tennis after her life partner, and the child’s father, became her coach, hitting partner and Mr. Mom. For awhile, they lived on $500 a month.

Then there’s Angela Braly, chief executive of health benefits giant WellPoint, whose husband left his family business for a more flexible schedule in real estate and teaching. They have three children.

How do we discuss the complexities of the modern balancing act without blunting our kids’ ambitions? I can hear them mocking us now: Settle for the mommy track early, dear, and save yourself a lot of angst. But that’s not the message. On the contrary, what’s important is figuring out what you want and planning for it, precisely so you don’t end up sidetracked.

Couples considering a family should talk openly about their expectations, too. You know the old saying: If you don’t know where you’re going, you’re sure to get there.

Anne Michaud is interactive editor for Newsday.