We spent a fortune on a charriot cougar wihch has suspension and all sorts! It fits 2 kids and is very very well made which it should be for the price.
They make a baby sling that can hold smaller ones, but I think our smallest was still >9 months before he could sit comfortably in it.
It is hard work towing it up hills and the kids always fall asleep immediately.
I expect we can sell ours for 75% of what it cost so all in all I think it has been a good buy, but TBH I don't think we've used it quite enough to justify it other than the fact that it is the only 2 child carrying thing he've had and we have needed it at times just for that. (with the wheel on the front as well that is)