A helmet includes a generally rigid outer shell and an inner lining. The inner lining includes one or more layers comprising foam or another compressible material. The outer shell includes a slot to facilitate placement of the helmet onto and removal from a head of an infant. The slot defines first and second portions of the outer shell on either side thereof. The slot includes a convoluted or keyed segment that defines a projection in the first portion of the outer shell. The slot is shaped such that one or more edges of the projection engage one or more edges of a recess in the second portion, preventing separation of the first portion from the second portion along the slot. The helmet may include one or more pressure indicators configured to provide an indication of pressure exerted by a head of an infant wearing the helmet.
