As more and more of us get multiple iOS devices , ( the iPhone, iPad , iPods) the days of sharing our iTunes accounts have come to an end.
You should have a separate iTunes account for every family member so that only your music , apps , calendar etc are on your device not on everyone else’s.
I am constantly talking to parents who have their childrens iTunes music on their iOS device.
There is also the issue with iMessage where text messages can end up on the wrong persons account.
When setting up the other iTunes accounts do it with a iTunes Gift Card , this works well with teenagers and children.