Thanks for your reply. They are playing on single player and are playing on the download .exe file. The mouse used to work fine in mine craft but now we seem to have the problem.
My Imac's mouse is not working properly in Minecraft since the update 1.5.1.
We cant mine blocks, cant kill anything. The mouse is working fine in all other programs. Is this a bug in the update? My boys cant play MC anymore and are very frustrated!