K.K.
My husband and I have been to Door County as a couple, and most recently, with our 17 month old son.
There are two farms to visit: The Farm in Sturgeon Bay and Plum Loco in Egg Harbor. Plum Loco has a kids play area and games, in addition to animals to feed.
Hands On Art Studio in Fish Creek is fun, but it might get to be a bit pricey with a large group.
People have mentioned PC Junction in Bailey's Harbor to me, but we didn't go. It has a train theme, and if you sit at the "bar" a train will deliver your food.
We enjoy Fred and Fuzzy's in Sister Bay for a casual, outdoor dinner. It's right along the water, so the kids can explore, and if you time it right, you can see the sunset over Green Bay.
Not Licked Yet in Fish Creek has yummy custard and a small play area for kids.
The Dairy View Country Store might be a fun stop if you are in the Carlsville area
Washington Island is nice, but you might try Peninsula State Park for biking too.
Have a great time!
K.