Let your child loose in the yard or on the playground and, chances are, he'll gravitate toward dirt.

Digging in the sandbox or squishy mud may not be your idea of a good time, but then, you're not a toddler. They love feeling all the different textures, and it's a thrill to get dirty (especially when their moms are always trying to keep them clean).

The good news for you: There's a lot to be learned in the dirt, like how worms wiggle and what happens to sand when it gets wet, says Nancy Close, Ph.D., assistant professor at Yale's Child Study Center. It also inspires the kind of creative play that's great for fine motor development  -- patting, shaping, filling, and dumping small toys. Other fun activities, like digging, carrying pails, and stomping a just-built castle, give larger muscles a workout, too (and are the perfect outlet for toddler energy).

As long as you make sure your child washes his hands (and, possibly, face and feet) when he's done, a little dirt definitely won't hurt.