Sprout, Nick Jr., and PBS have several educational games available for free online. They are age appropriate and contain no links to outside websites you wouldn't want your kids to visit.
The best site for educational games, in my opinion, is www.freerice.com. Not only does this site provide educational games, but it also helps feed the poor with rice.
The best computer games for kids in this age group are educational games such as star.com or Caiioo. Kids at this age are just honing in on their computer skills so less is better.
Whiz Kid - the best educational Android game for kidsAndroid Market: https://market.android.com/details?id=com.mobiwolf.whizkid
One can play online educational history games for kids on the 'Kaboose' website where they have a number of games. One can also play them on 'Kids Past'.
The Kidz Page website provides a wide variety of educational games for kids. One can find puzzles, coloring pages, clip art, word games and picture games.
There are many online options for educational games for young children. PBS Kids has it's own website at http://pbskids.org/ that includes many educational games for younger children. Starfall http://www.starfall.com/ is one of the best websites out there for really young children. It will help them build the skills to learn to read. Many teacher recommed Starfall and even use it in their classrooms.
Leapster math and spelling games. These are the best for this system and kids will have fun and learn at the same time with this system.
PBSkids.org/games is where you can find all sorts of games for kids of all ages that are super educational.
www.thekidzpage.com give a lot of educational fun free online games for kids. I'm sure they will find it very fun and excited about how many games there are.
The following website has over 50 games aimed for kids his age that are both fun and educational. It has a little something for kids of all interests. http://funschool.kaboose.com/preschool/games/index.html
roblox is the #1 site for online educational games for kids of all ages.
There is coolmath kids can learn things on that educational website