As another poster stated, your chances of getting a standard view at BWV, this late are pretty slim. A OKW studio will be the cheapest with BWV, BCV and VWL being the same number of pts, about 3-4 more per night, then OKW.
Considering the age of your child, I would try for VWL. This resort is just a boat ride away from MK (where you will probably spend a great deal of time due to your child's age) and it is right next door to FW campground which has tons of stuff for little ones to do. Also it is located closest to the largest number of character meals--something else the little ones love.
My next choice would be BCV because of the location, but mainly because of the pool. With only one child to watch, SAB is very enjoyable. Sit in the section that is zero depth entry and has a sandy beach for your child to play. Most of the little kids love this. You can even get a bucket and shovel included in a kids meal at the snack bar. BCV will also give you a great location to Epcot, MGM and the boardwalk (which is nighttime entertainment in itself).
BWV would be my third choice. It also has the advantage of being close to 2 parks and has a great Community Hall with many free activites. But your child is a little young to really appreciate all the Community Hall has to offer. The main pool slide is great, but again might be a bit too much for a 4 yo. We love the BWV,it is our favorite
DVC resort. But for a family with a 4 yo, I think VWL would be the best choice due to the close location to MK or BCV because of the pool.
OKW would be my last choice. OKW's studio would provide you with 2 queen size beds and an new pool sliide. But the location is not as easy to get to parks and dining options. Especially if you do not have a car, and are planning on using a stroller for your 4 yo. You will have to use buses to get everywhere. This means taking the child out of the stroller, folding it up, carrying the child, stroller and bags onto the bus and then repeating the whole thing again when you get off the bus, in order to get to your room. If you are not in one of the 2 buildings with elevators, you will then have to carry child, stroller and bags up staircases to reach your studio. Also there are not any nighttime resort activites to do at the resort like VWL, BCV and BWV have.