Letters and Numbers flash cards type programs. You'll be amazed how fast they learn.
Let them play with the mouse or keyboard, your system will be safe, and they will start to learn co-ordination.
Flip the pages of a book and read the story while little one watches the pictures.
Very simple paint programs. Lots of pictures to print too. A great way to develop co-ordination and imagination.
Just for fun, like Pin the Tail on The Donkey, but at this age they learn from everything they try to do.