Thule Sleek 2 Sibling SeatAnd when the family grows, so does the Thule Sleek 2 stroller: Add a sibling seat when your second child arrives, so both can ride comfortably, close together. Later, it can be expanded into a full double stroller with two toddler seats. Both seats include premium features like magnetic buckles, independent recline, and adjustable footrests, offering the same comfort and protection for both kids.