Themes, symbols, and epiphanies are literary terms that are used to speak about all different types of literary works.
A theme is the main topic or idea of a piece of literature. Themes are often big abstract ideas, and they tend to be emotions that are felt or expressed in the work. Oftentimes the theme is a recurring idea that is repeated throughout the story. This is the case in "Tears, Idle Tears
." The recurring theme of this short story has to do with how one handles grief, or how one should handle grief. This is seen in both Mrs. Dickerson and in Frederick. One can expand upon that and say the theme also speaks to how to handle someone else handling grief. Both themes are made clear at the beginning of the story when we learn that Mrs. Dickerson's husband (Frederick's father) died five years ago. This resulted in Frederick spontaneously crying quite often and his mother berating him for it. While it's a short story, it is clear that this sequence, and thus the theme of the story, plays out frequently.
An epiphany is the "ah ha" moment in a literary work. This is the moment that the character becomes aware of something important or gains some kind of critical knowledge. In "Tears, Idle Tears," this takes place when Frederick meets the woman at the pond who tells him that there is nothing wrong with crying or feeling emotions and people of all ages do it. Not only does Frederick realize that his emotions are not something that he should be ashamed of, but his mother realizes that she should not be shaming him for them.
Finally, symbols are a tool that an author uses to make something mean more than its literal meaning. An object, word, or phrase will be used to represent something else. In short, something seemingly simple has a greater meaning. At the pond, Frederick watches the duck swim by. The duck is simple and does simple movements. Frederick is a child, and his life should be simple and uncomplicated. The woman in the park also comforts and consoles him the way a mother should.