For kids who like trucks, BadrIT have made a great app just for you. It's called Thinking about Trucks. Check it now on the app store.
Route-Me is an open source native slippy map library for the iPhone, it replaces the MapKit framework that comes with iPhone SDK.
Route-Me works with OpenStreetMap, Microsoft VirtualEarth and CloudMade with support to offline browsing, on the other side the MapKit framework is limited to Google Maps and does not support offline browsing. During the development of an iPad application.