When you're paying top dollar for kids' clothes, you want a few bucks back for them.

"Kids go through seven sizes in the first two years," Minneapolis mom Dori Graff said. "So as a parent, you're always buying and you're always needing to get rid of things."

That's why Graff and her friend Mary Fallon created the iPhone app Itizen for parents to buy, sell and trade clothes for their little ones. Itizen is part eBay, part Facebook: The app combines an online marketplace with the ability to "follow" other users whose offerings match your needs and taste.

Here's how it works: You snap a picture of the onesie your toddler has outgrown. You name a price and a shipping cost, and then you add some descriptors that help shoppers find you, such as size, gender and brand. Then you post the listing to your profile.

Itizen is available by invitation only, but those interested can visit www.itizen.com to request an invite. The app has about 3,000 users so far.

Clothes are "the thing that floods every mom's closet space," said Joan Park, a New York City mom who uses the app. "It's really great because my daughter … there's no way she can wear all this, and it doesn't wear out. So I would love to let someone else get the life of the clothes, and then also get something back so I can invest in expanding her wardrobe for later seasons."

Park said the app attracts higher-quality items than you might find at a secondhand store. She gives baby clothes to other moms and to her church, but she saves pricier outfits for Itizen.

"It's a separate pile, the level-A stuff," she said. "It's worth my time to put it on the Web, and people will be attracted to it."

Graff, Fallon and Itizen CEO Dug Nichols said they're focusing on creating a community for moms to find bargains without sacrificing style.

With any app, "the early adopters are going to establish the culture," Nichols said. "Our early adopters want an outfit that would be $100 for half the price."

The social networking aspect is what makes the app promising, said Isaac Cheifetz, an IT headhunter and consultant in Minneapolis.

"In some ways, they're not really an app," he said. "They're a community that you access through an app. Let's say this takes off, and it has hundreds of thousands of young moms on it, transacting their stuff. … One could imagine Google or Yahoo or Facebook saying, 'OK, you've made yourself the preferred destination for moms,' [and buying Itizen]."

Park said the tight-knit Itizen user family makes the app more appealing than eBay, which she also uses, or other sites.

"There's a different relationship between moms," she said. "When you're exchanging with other moms, there's a real sense of community, like we really know each other."

Because the app is used all around the world, Graff said most users never have to set up face-to-face meetings — they usually use the shipping option instead.

The app is still in beta testing, but a full version will launch in the fall, available to all iPhone users. Then Itizen plans to move to Android, tablets and eventually Web browsers.

Itizen doesn't take a cut of sales on the app, so the founders haven't made money from it yet. They're figuring out ways to do so, but all they know so far is "definitely not ads," Nichols said.

Park said she appreciates the app for its clean interface but also the ability it gives her to display her style. And that, Nichols said, is what Itizen is all about.

"It's not just about the stuff," Nichols said. "It's about the people behind the stuff."