Sending my three daughters off to school this week was an exciting, exhausting, thrilling ride. Our brand new kindergartener took her first trip on the school bus. Our two year old got her first taste of preschool, and our third grader--the veteran--was back in the old routine. Getting up earlier, keeping track of a more rigorous schedule, and just adjusting to the demands of school all day energizes our family, even as it wears us all out.

There is nothing like back-to-school season. Even as an adult, before I had kids, I felt the invisible pull of the school calendar that controls our lives for so many years. The whole world is new in the fall. A buzzing energy, and a feeling of possibility, infuses the new routines.

The kids are busy, productive: three little girls out to conquer the world. They seem to have grown up overnight--especially the biggest sister, when she sits beside our kindergartener on the bus, gently guiding her younger sibling through her biggest life transition to date. It is a pleasure to see them glowing with pride.

But what lies ahead?

According to national research of girls in the United States, fourth grade is the peak year for girls' self-esteem. Nine-year-old girls feel great about themselves. But by fifth grade it is a whole different story.

What suddenly happens to girls when they turn ten? According to Anita Gurian of the New York University Child Study Center, just before junior high school, girls' self-esteem plummets. "Starting in the pre-teen years, there is a shift in focus; the body becomes an all consuming passion and barometer of worth."

A 2007 task force report by the American Psychological Association concluded that the sexualization of girls is a broad and increasing problem. At an alarmingly young age, girls start viewing their worth as tied up with sex appeal. They become passive, self-conscious, image-obsessed, and depressed. Ten years old is when girls start trying to look like the models they see in ads, and feeling bad when they don't measure up. They start pretending they are not that smart, because "smart" and "sexy" don't go together. Between 20 and 40 percent of ten year olds start dieting, Gurian reports. And 73 percent of girls between the ages of eight and ten dress and talk like teenagers.

There is an inevitable, poignant feeling about watching your kids grow up. Our happy, self-confident five-year-old, queen of the monkey bars, prides herself on climbing, jumping, and running like a nut. She puts on her own highly creative clothing combinations without a thought or a care about what other people might think is fashionable. She exudes pure joy--dampened, only briefly, when her big sister informs her about the somewhat limiting rules and social pressures of school.

At eight, already, I see my older daughter, who was also an exuberant playground athlete at five, becoming slightly more inward and self-conscious. Still a goofy little kid, she is nonetheless highly sensitive to the pressure to conform, to act like the older kids, and to discard "baby" stuff. This drive to grow up may be a kind of universal law of human development.

But the particular messages we send our daughters about what it means to grow up in our culture are not innate or natural or immutable.

Why on earth would we encourage little girls to become sex objects in fifth grade? And more importantly, what can we do to stop it?

This year, my eight-year-old daughter is going to join a group called Girls On The Run.

A neighbor has recruited me to help with the coaching. The organization was founded on the principle that girls who are making that fateful transition from third to fifth grade need all the help they can get feeling good about themselves.

Although she doesn't do the monkey bars that much anymore, as soon as I got my eight year old a pair of running shoes, she bounced out the door to "go running" around the block. Transformed by her own imagination, she has suddenly become a "runner." It took me aback to realize what a malleable, magical thinker she is. Still a little kid, she is open to the smallest influence and can completely change the way she sees herself.

We adults have so much influence, whether we realize it or not.

I have yet to receive all my "training" as a coach. But as a runner and a former coach of high school girls, I like the idea of getting girls to turn outward and take pride in their physical accomplishments.

Whether or not exhorting kids to feel good about themselves has any effect at all on their self-esteem (I doubt it), helping them to do something they can be proud of is bound to help.

I noticed this in the high school athletes I coached years ago. Girl jock culture is a powerful antidote to the preening self-consciousness of female adolescence in our culture. Girl athletes can take pride in their strength, not their sexiness--in being an agent, not an object.

The same is true of any activity that gets girls out in the world--learning about nature, conducting science experiments, making, building, and doing things, getting dirty--instead of staring at themselves in the mirror.

That is what I want for my kids: to keep alive the sparkle in their eyes--the pure, exuberant pleasure of unselfconscious physical play.

Now more than ever, thanks to Title IX and changing expectations for women, there is an alternative to the depressing passivity of the old feminine ideal. But at the same time, our toxic "sexiness" culture has kept girls from making the gains in self-esteem that First Wave feminists might have hoped for.

As my own daughters approach the fifth-grade tipping point, I want to do everything I can to help them overcome a culture that tries to undermine their world-beating spirit.