A child booster seat includes a seat body, a seat base coupled to and vertically movable relative to the seat body, and a height-adjustment mechanism mounted between the seat body and the seat base. The height-adjustment mechanism includes a support structure mounted co-movably to the seat body and formed with a plurality of positioning holes that are vertically spaced apart. The height-adjustment mechanism further includes a latching component coupled movably to the seat base. The latching component includes a stop piece for engaging a selected one of the positioning holes to releasably lock the seat body at a desired height relative to the seat base. The height-adjustment mechanism also includes a manually operable part for moving the stop piece away from the positioning holes to release locking engagement between the seat base and the seat body.