We will be taking our boys to WDW for the first time Summer 2019. They will be 9 and almost 6 when we go. This will probably be the only time we take them to Disney. That being said, what is the best resort option for boys that age. We definitely would spend time at the pool and money isn't necessarily an issue. Would also think about renting DVC points for the resort. Thoughts and reasons...GO!
I just asked my 9-year old son, who has stayed at every deluxe plus AoA and POR, and he said his favorite resort is the Boardwalk. He loves the proximity to DHS and EP, the pool and the entertainment at night. We've stayed in both the resort side and villa side and I personally prefer the villas (you don't HAVE to rent points to book these, you can book directly through WDW as well). If cost isn't an issue, consider a 2-bedroom villa at BWV. You will get 2 bedrooms plus a full kitchen and washer/dryer. If that's out of your budget, the 1-bedroom villas are great as well. Regular rooms on the resort side are also lovely!
If you will spend most of your time at MK, I would recommend the Poly (in fact, unlike DS9, this is what I would recommend!). I think for a one and only visit, staying at an MK resort is the way to go. It is so iconic WDW! The Poly is gorgeous, the theme is amazing, they have two great pools, good restaurants, the monorail (plus you can walk to TTC to catch the EP monorail). It is the first resort I stayed in when I was 9 years old and it left such an impact on me and has led me back to WDW over and over again. It is super magical! If cost isn't an issue, they have club level suites there which would give you some more space (they also have bungalow villas, but they are over-the-top expensive). The regular rooms are quite spacious as well. Again, if you are willing to spend the money, Club Level at the Poly is AMAZING and you may want to consider booking a club level room. I don't think your boys would ever forget their stay there.
If Poly turns out to be out of your price range and you still want to stay in the MK area, consider Wilderness Lodge or one of the villas at Boulder Ridge or Copper Creek (maybe a two bedroom or the new cabins!). Gorgeous, fun resort with boat service to MK.