Second Life, unfortunately, doesn't allow anyone under 18 (well, there's some complicated rule that can let in minors with some restrictions, but it isn't worth doing). There are other, more kid friendly virtual worlds.
It's a wise restriction - in Second Life you can go anywhere, and that includes some seamy corners. Since it's a world where everybody can see each other and interact, you're in the world with everybody else, good and bad. So letting kids loose in Second Life would be much like letting them loose in a city.
The Second Life viewer's not very kid friendly. I suspect it'd tax most 9 year old's patience.
On the other hand, you'd be more than welcome in Second Life, and yes, I can make you look much better than me (I actually have a sort of plain avatar. Since it's my work I want to seem 'serious'). And you could show your kids all the stuff.
I've spent a grand total of 4 months teaching children, so I asked on an educators list. After hearing 'hell no, don't let a 9 year old loose on SL', several K12 teachers suggested whyville. Other suggestions were poptropica and herotopia. I don't know any of them.
I do know
http://en.wikipedia.org/wiki/Roblox, it's a child friendly experience of building, much like Second Life, but not science oriented.
A childrens librarian friend suggested
http://www.stevespangler.com has lots of experiments you can do (even without buying the kits they sell). And going to the library, of course.
pbskids.org is a great science site.
This is a great book of things to do with a kid, many science oriented:
http://freerangekids.wordpress.com/2010 ... -ny-times/netflix! Zillions of wonderful science related 'stuffs' on netflix
Hey, want to actually DO some real, honest to goodness science for NASA?
http://www.zooniverse.org/They're asking people to help find things in all the data they're collecting. If you have the sort of kids who can get 'hooked' on something and spend hours concentrating, get them involved in moon zoo, a project to mark craters on the moon's surface from the LRO.
Zoo Tycoon! Great educational/science game. The original one was the best, the later versions became more complex, and are too complex for an 8 year old. You can find it for a couple bucks on ebay. Help the kids figure out how to draw fences. Tell them that shift 4 gives them money if they run out.
off the computer (yay! The computer's better for FINDING things to do OFF the computer):
chemistry-
Teach them about color mixing and paint. Watercolors (make sure you understand negative colors).
kitchen acid-base chemistry here:
http://fatherhood.about.com/od/teaching ... iments.htm Make rock candy!
Start a collection of the elements!
physics -
Look up water bottle rockets - they're simple to make, just valve from a tire and a 2 liter bottle. Tons of online info about them.
astronomy - binoculars are better than a crummy telescope, but naked eyes work.
If the kids go on an RV trip, the dark sky is great.
Stuff to do on a dark night:
Look at the moon - a printed map of the moon, a flashlight with a red filter (so you don't ruin your dark adaptation) and a clear night with a big full moon and you can find all the mares and stuff. Figure out from library or internet where the astronauts landed, and try to find those spots on the moon.
With a star chart find various constellations.
Lots of online programs will tell you where to look for the planets.
Lots of universities have observatories. A suprising number have open house, you can go look through the telescope at the sky.
Show up at the local amateur astronomy club.
Got an old film camera? Take a time exposure by leaving the camera out all night.
Point it at Polaris.
Out some place where there's a lot of space? Try making a model of the solar system to scale.
Hey, we're just a tiny little spec floating in space! (math's appropriate for a 9 year old for this).
biology -
gardening!!!!
find a BIG piece of ground that's bare or paved. Draw a blue whale on it full size with chalk.
Them things are BIG. Elephants are big too. I had fun once figuring out how to roast an elephant whole (turns out it takes months).
space technology:
Violate them gender norms! Get your granddaughter a model kit for a space ship. Assembling plastic models is a first step towards a life of making things for many kids. Make sure it's age appropriate in terms of complexity.
computers and programming -
Scratch! Great fun!
http://scratch.mit.edu/geology -
another great thing to do in an RV. You don't need to go to a special place - all you need to do is find a road cut.
that'd get ya started, but a bit of time spent surfing the net would generate a ton more stuff.
When I die I'm gonna be cremated. I can't stand the idea of spending eternity in a box with no wheels.