As advised above, I think you should buy where you want to stay because you will want that 11-month booking window. If you've never stayed at a DVC property, I can understand it being difficult to choose your home resort. I bought Bay Lake Tower without ever staying there & while the location is great (right next to Magic Kingdom), it's not our favorite resort to stay at & costs a LOT of points, so I ended up buying a 2nd contract at Boardwalk Villas. One advantage to BLT 2 bedroom, 3rd bathroom!!!
DVC resorts near MK via monorail besides BLT include Polynesian & Grand Floridian, but I'm unsure if that's available direct or just resale.
Boulder Ridge & Copper Creek are considered "near MK" but currently, you may need to bus to MK if the boats are not running at this time.
Boardwalk & Beach Club are walking distance to Epcot which we love especially during Festival season but they book up very quickly at 11 months, so not a lot to choose from at 7 months. You can also boat or walk to Hollywood Studios from BWV & BCV.
Animal Kingdom Kidani & Animal Kingdom Jambo House are great BUT they require a bus to get anywhere. There are no walking paths to parks or other forms of transportation. While some people enjoy the savannahs, we did not like being so isolated. 2 bedroom availability varies for these two depending on season & it will usually be the Savannah View rooms because they cost the most points. Any Value rooms are gone at 11 months all year around. FYI, Kidani 2 bedrooms also have a 3rd bathroom like BLT!!! I wish more DVC resorts had this feature!!!
Old Key West & Saratoga Springs are near Disney Springs, but to get to theme parks, you will have to take Disney buses. From SSR, you can walk to DS & there's also a boat from OKW & SSR to DS when weather allows, otherwise it's buses. We have stayed at SSR & didn't find the walk to/from DS appealing to us because everywhere we enjoy in DS, is very far from SSR. We find the bus drop off closer to where we want to be in DS than the walking path. I have heard the OKW rooms are huge since they were the 1st DVC resort but I've never stayed there myself, so I can't speak on it.
Riviera Resort is connected to Epcot & Hollywood Studios via Skyliner BUT to get to those parks at rope drop, it can be crazy backed up where bus transportation, if available, would be faster. The issue is you have to transfer Skyliner lines at Caribbean Beach Resort to EP or HS & lines get SO SO long with CBR, AOA, POP & RIV guests all trying to use the Skyliner. I haven't been tracking availability of RIV at 7 months but I know it costs a LOT of points to stay in a 2 bedroom. That might mean it will be wide open at 7 months but may result in a shorter stay.
You can see the 2021
points charts for each resort on the DVC website or WDWinfo website where you can see how far your points will go at different parts of the year. We usually like to travel to WDW in March which is the 2nd highest points season, therefore we only use our DVC for WDW every other year.
Hope you choose well for your family!