If you stay at the villas, there is a Community Hall with daily activities, crafts, video games, coloring stuff, etc. that they can do at any time of the day. You can check out DVDs and board games too (for a fee).
The main pool has daily activities like any other Disney resort.
The Boardwalk itself is just a shopping and restaurant area, so I wouldn't stay there for the Boardwalk entertainment. It's cute and fun to watch the performers. The carnival games are expensive, if they want to play carnival games then Animal Kingdom has better and cheaper.
We love the Boardwalk for it's location. We love taking the boat, eating at the different restaurants and shopping at all the shops. Even if we don't stay there, we make a point of going there for at least a day (we valet park).
But if you're going with the intention of "everything" is for the kids, then the Boardwalk isn't going to give you anything more or less than another Disney property. The value resorts are probably the most kid feeling if that's your goal.