A lock bracket assembly for securing a mattress support member of a crib to a headboard of the crib, includes an elongated bracket having a plurality of slots therein secured to the headboard, each slot having an enlarged mouth portion and a lower base portion in open communication with the enlarged mouth portion; a bar secured to the mattress support member, the bar having at least one mounting pin for insertion within at least one respective slot so as to mount the mattress support member to the headboard; and lift-prevention means for preventing escape of each mounting pin from the respective slots, the lift-prevention means including a lift-prevention opening in the bracket and an extension which is secured to the bar and which extends into the lift-prevention opening when the at least one mounting pin is inserted within the at least one respective slot.