The new "Bicycling" has an ad featuring Townies for kids: boys and girls models with 20 inch tires, and seatposts and stems with a wide range of adjustability. The combination of a seat position that permits full leg extention while pedaling and a "flat foot" when starting and stopping will make it much easier for kids to learn how to ride a bike.
My nine year old nephew is a good bike rider, but he dislikes stopping and starting because of the difficulty of leaning over on just one foot, and then getting the bike going again. I wish these bikes had been available a year or two ago.
The prices start at $180 for a one speed, and go up (and up and up). A $180 for a well-made bike that will fit for two or three years is a good deal. And, Electra bikes are built well, so a big sister can pass on an "almost like new" bike to little sister. A much better deal than buying a $50 bike that lasts six months.