Family Pack was a feature of the now-departed MobileMe. It does not exist in the iCloud world.
What do you mean by "their own sign ins to the same i cloud"?
How you will want to set up a set of iCloud and iTunes accounts for your family depends on what you want to accomplish and how you use the devices.
Example questions:
Does each kid have a different iPod, or do/will they share them?
Similarly, does each current and future iPhone and iPad have a single user?
Do some or all of you need to share calendars? Contacts? Email?
One common model for a family is for each family member to have a dedicated iCloud account on one or more personal (dedicated) devices(s) for mail, calendars, and contacts. They might well still use one common iTunes account for purchases; either everybody knows the password or maybe only the adults can do purchases. Sharing calendars, if needed, would be done with explicit sharing mechanisms.