HT4895: Using your Apple ID for Apple servicesLearn about Using your Apple ID for Apple services
Currently Being ModeratedNov 18, 2012 8:47 AM (in response to Jihamaki)
You could get them completely separate individual iCloud accounts if they are old enough (13). Or you can add up to three 'email aliases' - these are additional addresses (not accounts) which deliver into the same inbox as the main account.
You should however be aware before you start that once you've created an alias you cannot turn that address into a full iCloud account, move it to another account, or reactivate it if you delete it. This means that if you do this they cannot later use these addresses in their own separate accounts.
More information on aliases here:
Note that all new aliases will be @icloud.com addresses - @me.com addresses can no longer be created.