If you had just $50 to invest, would you put it toward your retirement or save it for your child's college education?

I know many parents would save first for college. It's natural. As parents, we often put our own needs last. Goodness knows I can't remember the last time I had a hot meal while eating with my young children.

If you've just sent your child off to college, you may be feeling like a martyr, having bypassed saving for retirement in order to give your child the best education you really can't afford.

But if that's what you're doing or plan to do, that's not a smart financial move. In this case, you have to put your retirement savings first.

What advice does a flight attendant give a parent flying with a child? In the event of an emergency and your oxygen mask drops down, you're told to place the mask on yourself first before helping your child secure his or her own mask.

When I first flew as a new parent and heard this instruction, I internally said, "No sir. I'm going to take care of my baby first."

However, as the flight attendant pointed out, I needed to secure my mask first in order to be able to assist my child. Failing to do so could mean we both might pass out.

Fail to adequately save for your retirement and your child (and his or her spouse, most likely) may pass out when you announce that you have to move in with them because you don't have enough money.

"The way many people think is they should get a house then save for college, and then they think about retirement," said Duane Meek, senior vice president for retirement plans for Nationwide Financial Services. "Retirement comes first and should be continuous. You really have other sources to finance your child's education. But when you get to retirement, if you haven't saved, you can't borrow that money because you can't pay it back."

Adults ages 25 to 40 were more likely to cite the need to pay for a child's college education as a reason for hindering their plans to retire.

Here's an example from Meek that might change those parents' minds. Suppose you're a 30-year-old parent who began saving for retirement the year your child was born. Assume you retire at 67 and had a starting salary of $35,000, which increased 3 percent each year until retirement.

You could have saved more than $750,000 if you had invested about 6 percent of your salary in a 401(k) and received a 3 percent employer match with a modest annual return of 7 percent.

Conversely, Meek said, a person who began saving for retirement after sending their child to college would have only saved a little more than $185,000 at retirement. That's 300 percent less money to live off of in your old age.

With the college year starting, Meek offers these tips on how you can save for your retirement and your child's college education: