there are many fun but simple flash games on the BBC website for kids:
http://www.bbc.co.uk/cbbc/games/?category=allgames

it's best to find the URL using your desktop; install adblock extension to firefox, then click the "block" tab at the edge of the game, take a note of the URL of the .swf, cancel the block, and then you can open that URL on the tablet in the web browser - I emailed my mobile address with the link, tapped on it in the email message and the browser opened and loaded the game!

I found that I needed to use full screen and a level of zoom to make it work properly. The more complex games got very slow