The secret to learning is to break what has to be learnt into tiny bits. A good way of doing this is to find one keyword from the topic that has to be learnt. Ask your children to tell you what the word means. Once they have told you what it means you can ask them some questions. You can ask them why the word is important and what it is connected with. Don't forget that dictionaries and encyclopedias are wonderful friends when you have to understand something.
Ask them to tell you one thing they know about the topic. Read the definition out loud. See if the definition reminds your children of something else that they have been taught. At this point they may remember that they have been taught about it. If your children still have no idea you will need to help them learn the topic from scratch.
Life isn't about finding yourself. Life is about creating yourself. - George Bernard Shaw