Mind maps are great fun and great for revision.
Get your kids to list all the key words in a particular topic. These will often be in bod in their text book. Write them on small slips of paper.
Put the topic title in the middle of an a4 sheet. Now put the key words around, and put those words which have things in common near to each other.
Then see how many connections you can remember between the key words.
So , for a topic like Photosynthesis a key word might be Cholorphyll. THis could be linked to another key word, cell (chlorophyll is found in cells) it could also be linked to another key word chloroplast, (chlorophyll is found in chloroplasts) is is also linked to the key word light (light needs to fall on the chorophyll to let photosynthesis work) The more connections you can make between the key words, the better you understand them.
If there are words unconnected to the rest, or only connected to the topic title, you don't understand them very well.
You can do them is different colours, add little drawings, they are a great revision aid, since they are active and also highlight what you don;'t yet really understand. They are also ideal for kids who don't like to write a lot, since you only have to jot doewn a few words and phrases.
Does that make sense???