I also set up a separate login for my DS at 3 and put the buttons on the toolbar that were appropriate for him. I purposefully did not even say the word Google to him because I didn't want to get into that.
I also would like to add that my son is one of those kids who can get obsessed with computer time and playing with the Wii. We let him play a certain amount per day and he can earn extra time with good behavior or being extra helpful. Also, I find if we are on vacation and I'm more lax about the rules after a few days he is not quite so obsessed.
