Bike for little girl

A friend is looking for advice on what bike to get for her little girl, and I haven't researched on little beginner bikes much. The girl is petite, turning 5 this week, can ride a bicycle, is pretty fearless, but has never ridden a dirt bike or quad before. I think she should get something that she can learn on, but still be able to ride for a while. She is looking for something used, as she doesn't have a large budget for this. Her husband is mechanically inclined, but they also don't want to have to spend a lot of time or money working on or fixing the bike. I think for now, it will mostly be ridden in their yard (in town). Any advice on what to consider (or avoid), and maybe even why, would be greatly appreciated. Thanks!