We've stayed at the Poly several times with small kids, and I can say, I don't recall a playground. There are poolside activities for kids, particularly geared to your kids' ages. Other than that, I don't recall specific organized activities for kids, but that may not mean that they're not there. In the lobby, there is a kids' section and they always have the tv playing something for them, kid sized tables, couches and chairs. They always have coloring pages out of Disney characters with crayons. They also have lei necklace/bracelet making with silk petals for kids usually always out too.
The Poly just lends itself to kids, I honestly think that the resort itself will entertain kids alone. There are great walking paths that are beautifully lined with the lush tropic vegetation, waterfalls, the lobby etc.
The volcano pool is fun, and you have the beach there where they can dig in the sand forever. It is fun to just hang out and watch all the comings and goings of the monorail, boats, etc.
One of my kids' favorite things to do was just ride the little "Willy Wonka" boats from the pier at the Poly to the MK, or the GF and take the monorail back. Believe me, this was just as thrilling as the parks at that age.
There is the Electric Light Water Parade each night that families always love too. If you want to spend the extra money, the surry bikes and water mice are a lot of fun too. You already mentioned the campfire and sing along and movie at Fort Wildnerness too, and they are great!
I would think there is more than enough to do with all that, remember, little kids just love doing the same things that they love over and over, and the fun at the Poly will be just as fun for them as the parks, that is what my kids always remember!
Hope this helps!
