Abstract: An infant rocking assembly includes a base, a sound-producing device for playing a soundtrack to produce a sound pattern, a top member which is movably mounted on the base and supports an infant-supporting structure such as a carrier seat or stroller, and a motor for moving the top member relative to the base in a manner which is synchronized with the sound pattern. Preferably, a stepper motor is used to produce complex movements of the top member and facilitate the synchronization. The stepper motor preferably rolls a truck between the base and top member to move the top member via engagement between upper rollers of the truck and camming surfaces of the top member. A microprocessor controls the motor and sound-producing device. A mattress support member and the low-profile rocking assembly may be positioned below an infant mattress to rock the infant mattress.