When you're shopping for your first stroller, you're naturally thinking about your first baby—not necessarily your second. Then, in seemingly no time, Baby #2 is on the way, but Baby #1 still needs the stroller, too. Now what? Many families purchase a double stroller with side-by-side seats, which works well for a period of time (and works great for twins). But when the older child graduates from stroller travel, you’re either back to where you started with the single stroller, or you’re pushing a double stroller with only one kid in it (resulting in unnecessary bulkiness, uneven weight...