Norms and rules are vital to inter-personal relationships, including within a family dynamic.
If you look at the process of socialization in a family unit, then you will understand that this is intrinsic to the family unit's role of preparing youngsters for the wider world, as well as maintaining order and structure within a close-knit group of people.
The rules and norms within a family act as a way for the family environment to help with socialization - reflecting how things wold work in the "outside world".
Here are some examples of socialization within the family:
Punishing children for bad behaviour, rewarding them for good behaviour, encouraging competition with siblings (this can happen without conscious encouragement, merely the result of being in a family environment).
