We will be staying the second week of September and will be the first time staying with
DVC. We will have a 15 month old and 5 year old at that time and don't know if it is worth it to just use the extra points for a preferred room.
The big appeal to Preferred is to be either as close as possible to Disney Springs (staying in Congress Park) or as close as possible to the Carriage House (staying in Springs). For your travel party, I suspect being close to Disney Springs isn't going to be all that important. So I think your decision is to book Preferred and request Springs, or book Standard.
So far, my stays have all been Standard, and I request "near pool." That is likely to put you in one of two places: the two buildings in Grandstand bracketing its leisure pool, or the two buildings in Paddock bracketing its feature pool. (It has a slide and a good QS location, and while it isn't *quite* as fancy/large as the main pool, it's very very nice.)
I think for your travel party, both of those locations could work, assuming you don't have mobility issues and don't mind pushing a stroller for a bit from time to time. Grandstand is the first bus stop, and quite close to the Carriage House. Paddock is either the 2nd or 3rd stop (I always get a space, but don't always get a seat) and there is a bridge (currently under renovation) that shortens the walk to the Carriage House.
Finally, the advantage of requesting "near pool" is that it gives you a very good chance of avoiding Carousel, which is the red-headed stepchild of SSR "neighborhoods".