To pick up on Matt's themes of writing on the experience of living with children as well as his most recent theme of violence coexisting with beautiful restraint, I would like to offer Sharon Olds's "The Clasp." It contains perfectly within one small stanza the complex ambivalence of parental love.
It begins with a swinging, back-and-forth rhythm: "She was four, he was one, it was raining, we had colds," (1). The rocking syntax of the four quick phrases helps the speaker lay out the facts of the situation while drawing the reader's ear and body into the music of the line. The following line relaxes into a longer clause, though it still resists a full stop: "we had been in the apartment two weeks straight," (2). The reader quickly understands that this lyric will be a confession and prepares to be sympathetic. Anyone, parent or not, who has spent five minutes with children can immediately see the inherent tension in the set up. The narrative then moves to the central action: the mother-speaker grabs the wrist of the older child to "keep her from shoving him over onto his / face, again"-- a perfectly understandable move (3-4)..
The real drama, however, occurs in less than a second, when the mother squeezes her daughter's wrist "to make an impression on her" (6); she reports savoring the stinging sensation, the "expression, into her, of my anger" (9). But the poem shifts again, from the "righteous chant" and staccato rhythms-- grab crush release-- to the parent observing her child experiencing her own revelation: "she learned me. This was her mother, one of the / two whom she loved most, the two / who loved her the most, near the source of love" (19-21). The intimate, innocent mother-daughter relationship deepens a level to envelop something dark. The mother watching the child learn this allows the reader to be present at the moment of the mother's realization. They hurtle together closer to the "source of love," and find "this"-- the speaker refers to the anger only with a pronoun, for the word anger cannot contain all of what "this" stands for: the moment, the learning of something big about the world from a child, the violence, the perverse enjoyment of it, the protecting of one child at the expense of another, and all the subtleties of emotion that occur in a moment of intense loving.
The exercise of writing this post reminds me of the frustration inherent in trying to "explain" a poem. So I recommend you find the poem, read it, and experience the "this" for yourself. I found it in Not For Mothers Only, which I am still reading with pleasure. You can find the full text on the web at http://www.poemhunter.com/poem/the-clasp/.