Instead, concentrate on working on expanding that variety to further ensure he is getting a nutritionally adequate diet. The one nutrient that I would be a little concerned about is iron. At 20 months, your son still needs iron from his diet. If the cereal he is eating is iron fortified than he should be okay. If he is not eating an iron fortified cereal, than consider a child supplement of iron.
Familiarity is the key to acceptance.
Those foods that you think he would like, and are child and age appropriate you should serve at family meals over and over again. At each meal you should include at least one thing you know he likes and will eat. This will keep you from looking like a short order cook, plus it is respectful of his likes and dislikes. You wouldn't dream of serving a dinner of only things your husband didn't like, and your baby requires the same consideration. However, beyond those one or two items, do not cave in and prepare a separate meal for him.