Try SERC (http://serc.carleton.edu/index.html), which provides lesson and unit plans for any geology topic, and breaks them down by appropriate age. I have taken a number and modified to make sure specific learning objectives are addressed and assessed- you can do the same!
Take children to park where there is a rock exposure or where is pile of rocks. Allow children to touch these rocks and individually describe them in writing as best as they can. Collect their writings and read them one by one. Allow some time for children to share and discuss their views. Lead the discussion and help them to discover new terms like minerals, matrix, surface texture, roughness, hardness, luster, color, odor, taste, porosity, magnetism, weight, density, origin, and age. This way you discover much more than reading text by others ...
Gunther's answer is excellent, as are the others since all schools have different situations. Find out what you can do and learn something about the capabilities of your audience first if possible.
We all learn by experience. Field trips are wonderful but if you cannot leave the school you could bring in rocks and ask the kids to bring in rocks from home. Fossils were always a big hit as are crystals and visible gold. Ask the kids to describe each rock while you summarize the information and translate into terminology, if your 8-yr olds don't write easily. If your class is large break into teams.
We also had great success with flume experiments (in the parking lot or playground). A bucket of unsorted material (dirt), a 6' long 4"+ diameter plastic pipe cut in half and water-- sample at top of flume, pour water onto soil, which runs down pipe, recreating sedimentary environment, repeat to make delta, etc. Compare the results to pictures, air photos to learn about scale and time. Make tsunamis in a wading pools. Ask questions to elicit data rather than lecturing.
We also grew salt and sugar crystals and compared them to natural crystals. Whatever you do, make it hands on and memorable.
Check with your local university. Ours has rock kits available for loan to take to grade schools. From there you can set up a fill in the blanks sheet for groups to work through. Kids are crazy about rocks but especially crazy about fossils so if you can get your hands on some fossils you will have their undivided attention. Eight year olds are really good at learning and discerning the difference between modern and fossil bone.
sometimes I have also to explain what is geology to childrens, personnally due to my double formation in geology and soil science, I try to explain them what is the difference between rocks and soils. Often people confuse what is the rock and what is the soil. So for me, it is essential to begin with the dissimilarities. Ask the children what is the rock? Some will tell you about the soil then try to show them the difference. Showed that the rock is actually "non-living", represent by "stones", while the soil itself is rather loose and colonized by organisms loke earthworms and roots. After this you can talk about the various rocks by using fossils for sedimentary rocks, pictures of volcanoes etc...
Few years ago, we realized simple experiments devoted to present geology to groups of young schoolchildren in the frame of the year of physics. We used many pedagogic documents and sandbox models to illustrate different tectonic contexts...
If you are interested by these productions, just ask me by e-mail ([email protected]), I will let you acces the whole set.
Children 8-10 years are interested in geology as a game. The problem is to do unto older children (teenagers) that geology is not a game but a multidisciplinary science.
The answers made are interesting already that the teaching of geology focused on children and adolescents is not an easy task.
The children of 8 years of age are full of curiosity and thus full of questions, the best way therefore to teach them is: first to let them ask questions.....Compile their questions and take the topics one by one. Select a topic that in your opinion would be easier for them to grasp. For example the questions can be: what is a mineral? for this you can take a few minerals from your museum, the simplest way will be to carry a hardness box and then you can explain many things about minerals the way you like taking into consideration their grasping capacity. Another question can be what is a rock? Take them out side of their class room and stand on the nearest rock but before that keep some rock samples in your bag and then explain the differences and types of rocks comparing them with the the rock on which you are standing. The question can be: how the Earth formed? For answer to this question, better take a video and explain gradually (that you can download from the net) on your computer. Similarly you can make them understand erosion, weathering, volcano etc. Sufficient material you can find on the net. Try to enjoy their questions and let them have fun....I am sure! we will not be able to give correct answer to many of their questions. All the best!!
Apart from the interesting materials listed on the websites of Haider Al-Ani-the symmetry can be initiated for children of 6-8 years making them paint and color symmetrical figures prepared (eg, butterflies, ...) and explain that by folding paper and with the help of scissors children (perhaps only the biggest) can be made symmetric motifs. Not always are with the crystallographic symmetry (differentiate axis 8 and axis 6, among others). This is economic.
I don't know if you still need info. for introducing geology, but briefly I have found out what best works in my area. First demonstrate some minerals, then some rocks then fossils. Turn lights off, hit a sample of pyrite ("fire rock") with a hammer and fire comes out! Then, use a sample of graphite to write on paper (here, students/teachers call 'pencil -lead" as Lead! Then pass around a piece of galena to show that "pencil-lead" is not lead at all - you would need two hands to hold pencil if it was lead! Then a demonstration of "bloodstone" or hematite by scratching it with a nail which makes it to bleed (but does not cry), putting acid on a shell (skeleton) that reacts and CO2 gas comes off, micas that are thin like paper but shiny and we use for Christmas paper/decorations, etc