The third paragraph of the body should contain the weakest argument, weakest example, weakest illustration, or an obvious follow up to the second paragraph in the body. The first sentence of this paragraph should include the reverse hook which ties in with the transitional hook at the end of the second paragraph. The topic for this paragraph should be in the first or second sentence. This topic should relate to the thesis statement in the introductory paragraph. The last sentence in this paragraph should include a transitional concluding hook that signals the reader that this is the final major point being made in this paper. This hook also leads into the last, or concluding, paragraph.
To have a coherent body paragraph, you would need to present the points of this story in a logical order, first explaining your main point that children should learn not to spend too much in one place, and then following with a chronological, clear order. You could explain that your son frittered his money away and then couldn't do fun things with his friends later. You might tie things up at the end of the paragraph with the argument that when kids learn this valuable lesson when they're young, they'll be more likely to be responsible spenders as adults.