The UPPAbaby VISTA double stroller is comprised of two different seats: the Toddler Seat, which fits only on the upper position, and the RumbleSeat, which fits only on the lower position. The two seats are different in size and are not interchangeable. The smaller RumbleSeat has a weight limit of 35 pounds, while the Toddler Seat holds up to 50 pounds. Both seats can be reversed, reclined and used in a number of configurations. See UPPAbaby VISTA Toddler Seat vs. RumbleSeat for more information.