... the oldest of which is now in kindergarten. Our current "computer policy" is a not-without-mom-or-dad policy.
The 5yr and 4yr old have a few age appropriate games that we will let them play relatively unattended and with permission (they love bejewelled, ms paint, and anything Blue's Clues).
As for the internet, we are big fans of Google's video search for finding things like
rocket launches,
the mentos experiments,
painting elephants,
erupting volcanoes, etc. We also look up articles on wikipedia to answer questions (usually of the science and nature variety). But we never let the kids drive and the computer screen is always locked when not in use.
The why's aside, here is what we have done for my 5yr, 4yr, and 2.5yr old regarding email.
1. I bought a google apps domain ($10/yr)
2. I set up gmail accounts for each kid (first names only)
3. I set up the password (remember "not-without-mom-or-dad" yet)
4. I set up the contact list (mom, dad, grandpas, grandmas, a few friends.
5. I set up a the following gmail filter for each account
(-(mom@address OR dad@address OR friend1@address))
with the action "DELETE". This takes any email not matching the addresses in the list and deletes them.
6. I set the "view" to be standard HTML - it's not perfect, but it is fewer gadgets and options.
7. I created shortcuts to their accounts on the desktop.
8. Finally, we sit down and check email about once every 2 or 3 days - together.
It's not perfect - I wish there was a simple way to compose an email based on selecting a picture of the recipient, but then again the five year old is the only one who can type his own email anyway.
As for the future, I am scrounging parts to build a "kids" computer. But that is mostly to keep their grubby fingers off the same computer my wife uses to do finances. By the time they are in their teens, I hope to have decent smart-terminal setup where we can use a central server to monitor use, filter sites, store pictures/video, etc.