If your food supply in the bin is good and you have about 20-25% of your villagers working on farming, I wouldn't worry too much about the fact that you don't see crops on the farm. The crops grow on a cycle, similar to a real farm. Depending on how often you're checking, you may just be 'missing' the crop cycle. The crops can be harvested fairly quickly if you have more than about 12 villagers. Once they are all harvested, there will be no more food from the farm until the next crops appear. By the time you get to 15, you really need fishing in order to grow your village and maintain an adequate food supply.