Ask any parent: children change your definition of what’s important.

With kids, a baseball game or a ballet recital trumps nailing the next promotion. In short, it’s no longer in your best interest to put in crushing hours at the office.

But you need the money so you’ve got to work. The question: how can you negotiate a shorter work week so you can better balance career and children?

“A lot of people don’t think a flex schedule is possible so they don’t broach the subject with their employer,” says Laurie Lopez, general manager at Winter Wyman Technology Contracting in Waltham, Mass.

“That’s a mistake because companies spend a lot of time and money to recruit and train quality employees,” Lopez adds. “Smart employers know it’s easier to retain happy workers than to constantly hire new employees. When you discuss the issue, make sure you have a plan and make it clear how your new schedule benefits the employer.”

In an effort to retain talented employees, many companies offer telecommuting, flex-time, reduced hours, job sharing, flexible holidays and extended vacations. Some companies provide on-site daycare or kick in a percentage of childcare costs.

Both men and women sometimes need a flexible work schedule, but caring for the kids still tends to fall to the mother.

When talking to your boss about something other than a traditional 40-hour week, make a proposal – not demands. Pounding desks and kicking over chairs will defeat your efforts.

The key: know what you need to get what you want. That’s simple enough but many employees haven’t considered their needs beyond reducing their hours when making a pitch for a flexible work schedule and overlook a basic point: your plan must benefit the company, too.

Nail down these points to improve your chances of making a successful pitch for a non-traditional workweek:
 

• Make a list of how your proposed shorter workweek will benefit your employer and your family.
  
  
• Check with co-workers and the personnel office to find out what the company has done for others and what might be possible for you.

• Develop a detailed plan and put your proposal in writing.

• Be sure to talk to others who have negotiated a flex schedule. Ask how they did it – and learn from their mistakes.

Your boss needs to know how you’ll put in the requisite number of hours and how you’ll keep the work flowing. If your company needs someone to work early or late and if either morning or evening fits your schedule, you may have a match. Think about holidays that fall on workdays -- can you help your boss out?

You can’t simply tell your boss you want to reduce your hours to 20 or 30 a week. Your boss will ask a basic question: what’s in it for me? If you don’t have an answer, you’re dog meat. Propose a trial period -- and be prepared to turn handstands to make it work.

Remember: you will take a pay cut. Make sure your household budget  can take the hit and that you have a saving reserve. Do the math because returning to the boss with a revised proposal to fix the mistakes of your initial plan will undercut your position and make it more difficult for others to work a flexible schedule in the future.

Many large companies, including Abbott (ABT), Eli Lilly (LLY), Genentech (DNA) and Johnson & Johnson (JNJ), have established themselves as family friendly and therefore good places to work.

You don’t have to be the office genius-in-residence or a key employee to get a revised schedule that allows you to spend more time with your family. However, if your employer rejects your request to work fewer hours, it may be time to start sending out resumes and find another job.

The free market makes it possible for you to vote with your feet. Savvy employers know this and, when possible, will work with solid employees to develop a work schedule that fits the needs of both sides.

“Hiring is expensive and smart companies want to keep people they’ve trained,” Lopez says.