A bicycle (1,51,61,81,91) for children that can “grow” with the child. The bicycle comprises a frame (3,53,63,83,93) having a seat-tube (5). The frame has a front wheel (11), a rear wheel (13), a pair of handlebars (19), and a saddle (15) having a seat-post (17) for insertion into the seat-tube. The bicycle comprises a detachably mounted drivetrain (27) for releasable engagement of the frame to allow conversion of the bicycle to a balance bicycle or a pedal bicycle. Furthermore, the bicycle frame itself is height-adjustable to allow adjustment of the seat tube's (5) height above ground and reach-adjustable to allow adjustment of the distance between the saddle (15) and the handlebars (19). By providing such a bicycle, the bicycle will be convertible from a balance bicycle to a pedal bicycle and will also have a frame that is adjustable in height and reach. This bicycle will be suitable for a wide range of child heights and cycling abilities.