I stayed at BC and WL in one trip one year - a week at each - not at the villas but the hotel, but still, same facilities. My eldest was 5 or 6 then and he loved WL - it's the only resort he remembers.
The WL pool is nice for young kids and there is also the paddling pool. Whilst Stormalong Bay is great, it is so huge that it is hard to keep an eye on young kids.
They used to have a character breakfast at WL, which was good. The character breakfast at the BC is great if you eat at a late time both for character interaction and food quality.
The boat trip to the MK is excellent for little ones - this is the park where you will spend most time at at that age.
The cycle paths at WL are great for taking young kids on.