Many families struggle to pay college expenses for one or two children. Certified financial planner Sarah Carlson, mother of two sets of twins, will soon have all four of her children in college at the same time.

The older twins are already there, to be joined soon by the younger two. But years ago, Carlson started teaching her children how to get an affordable education. One of the first steps was making clear what she would contribute.

“I let them know early on what I was comfortable spending and what I wasn’t,” says Carlson, who’s based in Spokane, Washington.

The time to spell out exactly how much education you can afford is long before the first application essay is written. This summer could be a great time to talk with younger teens about the reality of college costs, how much they can expect you to help and affordable alternatives that can keep your family from drowning in debt.

Start with sticker prices

A good way to start “the talk” is to have your children research prices for a variety of colleges – public and private, in state and out, large and small. Sites such as CollegeData show total cost of attendance, including tuition, fees, room and board, books and other expenses.

That should be an eye-opener for your children, and perhaps for you. Few people pay the sticker price, but the actual cost can vary dramatically based on your family’s resources and the school’s aid package.

Next, use each college’s net price calculator to see how much your family might pay. These calculators, required by federal law, vary in their complexity and accuracy but can give you a rough idea of the bill after possible financial aid is deducted. You may find, as Carlson did, that some private colleges could be less expensive for your family than some public ones.

Assess your resources

Families spent an average $19,100 last year on an undergraduate education after scholarships and grants were deducted, education lender Sallie Mae reports. Parents shouldered most of the burden, with $5,109 paid from their current incomes, $3,782 from savings and $2,648 from loans on average. Students borrowed $3,833 on average, and contributed $3,339 from their own income and savings.

When totaling your available resources, be cautious about tapping retirement funds or borrowing too much. Your child has a working lifetime ahead to benefit from the education and pay back any loans. The time until you retire will be much shorter.

Set expectations

Most teenagers can’t “work their way through college” or pay for an education entirely on their own. Working too many hours can result in lower grades and increase the odds of dropping out. But it’s OK – smart, even – to expect them to contribute something through part-time or summer jobs, says CFP Leon LaBrecque of Troy, Michigan. All three of his children worked summer jobs, and two worked multiple jobs during the school year.

“Busy people get more done,” LaBrecque says.

If your child plans to borrow, they probably should stick to federal student loans, which are limited to $5,500 the first year and no more than $31,000 for a typical undergraduate education. Scholarships can be another way to help pay the bills.

Talk about the gaps

Discussing options can keep your child from fixating on an education you can’t afford. Alternatives might include choosing the school that gives the best financial aid, starting at a community college or living at home rather than in a dorm.

Also, be careful about making promises, since life happens. A divorce left CFP DeDe Jones of Lakewood, Colorado, with less money for college than she’d hoped. Each of her twins, now 26, received a fixed amount for college that would allow them to graduate without debt, but only if they chose in-state schools and lived at home.

Both did. Her daughter stretched her college fund to pay for six years of college after she switched majors from nursing to computer science. Her son got both a bachelor’s degree and a master’s in just four years and is now pursuing a Ph.D. on a fellowship.

“They really took it to heart,” Jones says.

Liz Weston is a columnist at NerdWallet, a certified financial planner and author of “Your Credit Score.” Email: [email protected]. Twitter: @lizweston.