Defnitely get something that will take the two of them. If you have them really close, your first baby may not even be walking by then, let alone be able to walk a long distance. Then they may still be little enough that they fall asleep while out, so you will need something for them to be in while they sleep. My first 3 were all 20months apart and I used one of those pram skateboards and that was enough for me - they could get off and walk sometimes and then just ride on the board when they were tired, but as soon as we got back to the car they were knackered! So in hindsight I probably could have made use of a pram with at least a toddler seat, if not a double stroller.