Mud pies. Puddle slogging. Dirty fingernails. Grass-stained knees. They're all in a day's work for my boys, proud members of the Unwashed Masses of Childhood.

Just when I'm feeling a bit too relaxed about my hands-off approach, arrives a serious crop of scientists to back up my instincts. Don't you just love when that happens? Turns out, getting dirty is critical to your kids' healthy development. Send them outside to play, experts say -- and don't wash them up before dinner.

"Dirt is good," says immunologist Dr. Mary Ruebush. "If your child isn't coming in dirty every day, they're not doing their job. They're not building their immunological army." And if you're not letting them, you're not doing yours, either. Her advice: Let kids play in the dirt, vaccinate your kids and use regular soap and water.

In fact, that consumer-grade antibacterial soap I find so smelly is no more effective in preventing infectious disease -- and doesn't even remove more bacteria -- than plain old soap. Trouble is, it can also breed "super bugs" that our bodies (and antibiotics) can't fight.

Richard Louv, author of Last child In the Woods: Saving our Children from Nature-Deficit Disorder, links the lack of nature in kids' lives today to some of the most disturbing childhood trends: Obesity, attention disorders and depression, to name just a few. The great messy, dirty outdoors is vital for healthy childhood development. Adults and kids who spend more time in nature have less stress, and some say it reduces ADD symptoms in children as young as five.

Maybe we don't all live in a world of grassy meadows and watchful neighbors, not to mention rambunctious play, bloody scrapes and broken bones can (and should) be avoided, right? Nah uh, says behavioral neuroscientist Sergio M. Pellis. Sure, you don't want them in the ER, but too much protection "simply defrays those costs to later," Pellis says.

Now I get it. You don't want to clean it all up. Who does? And that's the point. Just remember this pearl from Phyllis Diller: "Cleaning your house while your kids are still growing is like shoveling the walk before it stops snowing."

Do you let your kids get dirty?

Victoria Scanlan Stefanakos is editor of Project Homestead.