S.K.
We have a Joovy Caboose stroller that we got at a consignment shop so it is an older model. It has a place for the older child to stand on a platform or a "jump seat" -- the seat slides back and forth to allow the child to either sit on it backwards (ie facing the person pushing the stroller) or stand on the platform. The front seat on the one we have we now use as a regular stroller seat with a 5-point harness but it had an adapter for the front seat that accomodated our infant carseat. Once our daughter was finished in the infant seat we unsnapped the attachment and simply use the stroller now with the little one sitting in front and the older one either standing on the platform or sitting on the little back seat.
My older daughter never really liked strollers past the time she could walk on her own so I thought the sit and stand would be a good option. We also got a double jogger because once her little sister was born and getting rides, the older one decided she wanted to sit too! :)
Good luck!