A brake device is disposed at a child carrier including a frame and at least one wheel unit that includes a hub and a plurality of spokes radiating from the hub. The brake device includes a base unit, an operable unit, a brake unit, and a positioning unit. The base unit is connected to the frame and is formed with a first guiding groove and a through hole. The operable unit is pivotally connected to the base unit and includes at least one side wall formed with a positioning hole and a second guiding groove. The brake unit is disposed slidably in the first and second guiding grooves. The positioning unit is disposed in the through hole and includes a positioning component and an elastic member elastically abutting against the positioning component.