My kids have decided that they also want to play. They live in the same house, but use different machines. Do they need to use a different account from mine, and if they do, can I refer them to take advantage of the refer-a-friend? Sorry for the stupid question, but want to be honest and pay if I must. Thanks, Smudge.

One of your children--given that they are still considered a minor at this point in time--may use your account to access World of Warcraft; any remaining parties must have have their own account if they wish to play.

From the Terms of Use:
http://www.worldofwarcraft.com/legal/termsofuse.html

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Q u o t e:
Eligibility.

You represent that you are an adult in your country of residence. You agree to these Terms of Use on behalf of yourself and, at your discretion, for one (1) minor child for whom you are a parent or guardian and whom you have authorized to use the account you create on the Service.

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And...

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Q u o t e:
Establishing an Account.

During the registration process, you will be required to select a username and a password that are unique to the Account (collectively referred to hereunder as "Login Information"). You may not share the Account or the Login Information with anyone other than as expressly set forth herein.

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With this, Smudge, you are most certainly welcome to use the Recruit-A-Friend program to equip your family with new accounts: http://www.worldofwarcraft.com/account/recruit-a-friend.html