I need to write a Thesis statement on the effects that domestic violence has on children in that relationship and I am stuck.
It is impossible to right a thesis statement until you know what point you want to make and how you are going to support that point. This sounds as though it's an assignment to write a research paper. Have you done any research yet? That research should give you some idea what effect domestic violence has on children. Once you have an understanding of that, you should have no problem writing a thesis statement.
Generally, a thesis statement provides the main idea you want your reader to understand after reading your paper. That idea might be that domestic violence has terrible effects upon children. Or your main idea might be to advocate for funding for better programs to prevent domestic violence because it affects children so negatively. Whatever your main point might be, your thesis statement should state that idea and then give the reader a kind of outline of the ways you are going to support that idea. Sometimes a thesis statement will take the form of "X is true because of A, B, and C," with X being your main idea and A, B, and C being the points you will make to support that idea.
Do your research, and you will find it easy to write that thesis statement.