You can choose any topic relevant to developmental psychopathology. If you have any questions about the relevance of your topic, please talk to me. I suggest you pick a topic that you would be happy to expand on for your final paper, which will be longer. The easiest way to choose a topic is to pick a disorder from the textbook and do a little research to see if there is a particular topic which interests you.
Please identify key questions, problems or issues related to your topic. These can be inter-related. For example, you could discuss Autism. Issues you select might include whether autism is really increasingly common, why more children are being diagnosed with the disorder than before, and whether or not whether or not vaccinations are really a cause of autism.
You do not need to use any sources outside your own experience and the textbooks for the first paper, but it might help to look for some. Internet articles and summaries will be fine for picking topics and offering opinions that interest you. You do not need to use primary source materials (for example psychology journals) for this paper, but I will expect that they will used in the second (and final) paper.