If the oldest of 3 is old enough to walk most of the time, I'd consider a buggy board. We used one when we brought a nephew a few years ago, when DS was still small. Nephew was 5 at the time, he just stood on back and hitchhiked. When he got really exhausted and fell asleep on the way to the hotel, we put him in the stroller and used a sling to help carry DS.
http://www.dmart2000.com/bugboarbylas.html
There is also a variant gadget called the Seat-2-Go; the older child can actually sit with that one. I don't have any personal experience using it:
http://www.dmart2000.com/seat2goatstr.html
Note on a couple of things in previous posts:
You can use a big Sit n' Stand at the parks, but you can't get them on parking trams, and they are very difficult on busses. I've seen people use them, though; they drive to the parks, drop off one adult and the stroller at the "drop-off" area, then circle around, park, and the rest of the party takes the tram and meets the adult with the stroller. For MK, the ferry works better than the monorail.
Unfortunately, generic baskets that can attach to any stroller are not normally sold in the US; there is little market for them, as almost all American strollers are sold with the basket already on. You can order them from stroller mfrs., but they run about $20 + shipping, and for a cheapie umbrella stroller, that's more than the cost of the stroller itself. You can, however, buy net bags to go on the back, or make a simple basket; I've made several. The clip-on umbrella will run about $7 from Graco; most baby stores have them.
For anyone who wants to make a simple basket: you need a mesh laundry bag, 3 yds of 1" polypropylene webbing, and a packet of heavy-duty snaps or sew-on velcro. Measure the area inside the stroller legs (above the flat-x cross brace), then subtract 2" from the size on each side. Cut that square, double, out of your mesh laundry bag, then cut 2 strips of webbing the length of each fabric edge, plus 3". Sandwich the 2 pieces of mesh between the strips of webbing, so that the webbing forms an edge binding, and zigzag stitch across it thoroughly. The extra 3 inches on each side of each corner will accomodate your snaps or velcro, to fasten the basket to the stroller legs. The mesh will stretch a bit under the weight of what you put in, so the basket will not be really flat. Also, to seal the cut-ends of the webbing, pass them *briefly* through a flame; the webbing will melt, sealing the raw ends so they don't unravel. (The doubling of the mesh is needed, because that size mesh is looser than the sort normally used for stroller baskets, it will stretch too much if not doubled. Regular stroller mesh is not sold in most fabric stores, and is very expensive when it is.)
