My husband was much older than I am. His children used to introduce me to people as “Dad’s wife” because I am only a few years older than they are.
Now that he has passed away they do not know how to refer to me. “Stepmother” does not seem right because we are so close to the same age.
Queenie, do you have any suggestions?—His widow
My condolences on your loss.
They could refer to you as “Dad’s widow” or “my late father’s wife” or simply by your name, with explanations about the relationship coming later.