You don't have to wait until the children are in second or third grade to write a report. Get them in the habit when they are very little, just starting to talk in complete sentences. Really, a report is just putting into writing what you know.
Toddlers know a lot.
When they are able to talk in complete sentences, tell them you're going to help them start a journal. Let them tell you about their day, or about a special event. As they talk, type the material into your computer, or write it on paper. In these early journals, don't worry about getting the facts straight. If they want to say they saw a green chicken talking to a purple elephant, let them.