Kids can get this from being in the womb. Basically they position themselves with the curvature of Mommy's belly. Their feet form to that curve. I was told by our pediatrician, "Don't worry about it. His feet will fix themselves over time."
He ended up going through teething and was really off balanced. He literally tripped over his own foot and ran smack into my sister's coffee table. We had to take him in to get stitches in his forehead.
Later we saw a different pediatrician to get Isaak's stitches out. Our doctor was not in the office that day. He told us to see an orthopedic doctor. The orthopedic doctor wrote us out a prescription to get special shoes to wear. I was freaking out! I was thinking my son would have problems with walking, running and was worried about the cost of special shoes. They basically looked like they were on the wrong feet. They were supposed to mold his feet back to being straight. Cost: $100, that insurance company does not cover. Insurance believes that all special foot ware is cosmetic. Therefore they won't cover the cost.
We went in for a check-up back at our pediatrician. Our doc said that those shoes do nothing to fix their feet. It's actually better to let them run around barefoot or in soft shoes like Robeez. We went back to wearing shoes like these:
Today my son Isaak is now 3 years old. His feet look just fine.
You can find more information out about bowed feet here.