The previous post did a very nice job in addressing the ideas of a thesis statement. I would suggest broadening this a bit to include Gordimer's work. Your thesis statement in terms of its connection to this text could connect to the idea of how the family's actions are motivated by something other than pure love for one another. Another thesis statement could revolve around the idea that creation and destruction are closely intertwined in the story. Another thesis statement could be centered on the political context of the work, itself. What might the work be saying about a post- Apartheid South Africa? These could be areas where thesis statements about this work could be quite powerful and compelling.
A thesis statement is your main argument. What makes a thesis statement a good one is the following:
1. It must be debatable. If it is not debatable, there is no point in writing about it.
2. You must have good reasons for why you believe in what you do.
3. Also to make your thesis stronger, you want to consider other view points, especially people who may not agree.
Here is an example:
"The Athenian Empire was not democratic." Now what you need to do is give a few reasons why you this this thesis is true. For example, you can say that they were imperialistic, that they had slave and they did not treat women with respect.