Stick to the research questions. Once the reference material and index cards are in place, your child can work independently. As he reads, remind him to note only details that help answer the questions at the top of his index cards. No matter how interesting the fact, if it doesn't answer a question on one of the index cards, it shouldn't be written down. Compiling note cards will also help your child get a sense of the amount of work needed to complete the entire report.
Research reports can be overwhelming monsters for kids.
Don't be frustrated if, in the beginning, you seem to be the one holding the process together - or if your child thinks you're a nag.