Ask HN: Computer setup for preschoolers? (age 3-5)

I'm looking to setup a lounge-room PC for use by my pre-school children to educate them in computers, and I'm looking for first-hand experience from parents.

Both my children (3, 5) have had iPads since about 2 (and plenty of dead-tree books, read to them by us) however I'm looking to teach them how to use a keyboard/mouse and basic computer usage.

I've seen there's a few Linux distributions focused on this purpose, but they all feel a bit 'unpolished'. I'm not too bothered about the OS, but the important things are:

* Internet usage is restricted (i.e. only available when parent is there, and even then only 'safe' things are available) * Impossible to break the computer (i.e. no amount of clicking and bashing on the keyboard will render the machine inoperable) * Ideally feature mainstream apps * Be able to connect to my TV with a cordless mouse + keyboard

What do you do?

Thanks in advance HN