XNA Game Studio
Well my sons had a great time last year getting stuck into Scratch, so I thought it might be worth moving them up another level to a more fully blown game development environment
http://www.microsoft.com/express/gamedevelopment/
Our first problem was our graphics card was not up to scratch, so having replaced that just before xmas we are now all set to get started in the new year.
We are going to use the c# version rather than c++. It is a major learning curve compared to Scratch, so it will be interesting to see how they get on. I will keep you posted.