Email server configuration for screening email on private lan

Hello,
I would like to set up a mail server in my home LAN where I can set up accounts for my children so that they can start learning how to use email but I want to have full control of the email they receive and send. Is there a configuration you recommend or a reference where I can read about such arrangement? I am sure somebody else has thought of this but I haven't found this specific topic yet.
THank you in advance for your help.

Well... couple of questions for you...

1) What OS would you be running?

2) What do you mean by having full control? You can have full control over any email account you set up for them. Or what I have personally done for my kids is to set them up with an email account which gets delivered to me as well in my inbox. I then can see who's sending what and let them know whether they have email or not so they can check themselves on their computers. For this, I do have my own DNS and email server, but you can do this with your own domain and a webhost as well.

3) As far as what configuration to recommend, explain exactly what it is you want to do...