A lock for a height-adjustable crib or playpen requires two distinct manual operations in order to release the lock on each crib leg. Each lock includes a rigid metal bracket which engages around the extensible part of the leg and is pivotally connected to a crib corner post. The bracket has a nose which projects into one of a series of openings in the extensible part of the leg then the bracket is swung against the leg part to prevent movement of the leg part relative to the post. The upper edge of the bracket is slotted to receive a latch pivotally connected to the corner post just above the bracket. The latch drops into the slot when the nose is engaged in one of the openings so that the bracket cannot be moved.