Family is a Registration Type available within Register Now. It is useful for events that have a very high proportion of entries of families where it make the process easy for the Family Administrator plus it allows for special family pricing.
The first thing to decide is what age to split Adults and Children (the default is 18 - i.e. anyone 17 or younger is a child, anyone 18 or older is an adult). There is only one price split here - you can't have additional pricing age brackets within Families.
Then you decide how you want to price families. A family registration fee can be a set price for the whole family (and additional family members are then charged per person), or each person can be an individual price. The actual prices are set on the Event Prices Tab.
If pricing is set Per Family, you need to determine how many Adults and how many Children are included in that price. Then on the Event Prices Tab you will set the bulk Family Price plus the price for Additional Adults and Additional Children.