A support insert assembly including a first member having first and second curved side surfaces parallel to a first direction, first and second planar partial ring-shaped surfaces connecting the first and second curved side surfaces, and first and second end surfaces connected to the first and second curved side surfaces and the first and second planar partial ring-shaped surfaces; and a second member having a third curved side surface, a straight side surface parallel to the direction, and first and second hemispherically-shaped planar surfaces connected to the third curved side surface and the straight side surface and parallel to one another, where the first and second members are arranged in an opening tar a seating arrangement for the infant to form a space enclosed by the straight side surface and the first curved side surface, and the space is arranged to receive and support the infant.