When it comes to retirement planning, there's one maxim that's worth repeating a thousand times: The earlier you get started, the better. There's no amount of ink that can be spilled to truly capture the power of compounding returns over time.

Knowing how important that early start is, unexpected expenses early in one's working career can have ramifications that filter down for years to come. Shockingly, the one thing that young families across the nation spend the most money on every year comes as a complete surprise -- and it's not housing, food, college, or health care.

The culprit: finding someone to watch young children during the day while parents are off at work.

How much does this end up costing? As I've shown before, the costs vary wildly by both region of the United States, and whether you are in an urban or rural location. But a recent survey conducted by Care.com (NYSE:CRCM) says that the average family can expect to pay $18,000 per year in child care.

Let that sink in for a minute.

Chronically Underprepared
As a father of a 1-year old myself, I can sympathize with parents-to-be spending most of their mental energy on how great it's going to be to have a child, without thinking twice about the cost of child care. "We'll figure something out..." actually makes a lot of sense when you're in the nesting stage.

Apparently, I'm not alone, as 42% of families don't budget at all for child care, and 75% are "shocked" at the total costs, according to the Care.com survey. With the majority of households having no parents at home during the day, that means there's a serious reckoning happening across the country when maternity leaves end.

Check out the slideshow below to see how you can save money and help make sure that having a child doesn't mean retirement planning needs to be put off indefinitely.

Brian Stoffel has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.