Nuclear family
A nuclear family is a household consisting of two parents and their legal children (siblings), as distinct from the extended family. Whilst the family is a near-universal cultural phenomenon, nuclear families do not form the family unit in every society. Nuclear families are typical in societies where people must be relatively mobile -- such as hunter-gatherers and industrial societies.
Research
Research [1] is claimed to show that the nuclear family is better than any alternative arrangement to ensure that members of the next generation obtain the emotional support they need, and help to find occupations. Whilst this may be true, statistics collected by the British government can be used to support the argument that family's involvement of the extended family might help in keeping nuclear families intact. So whilst the model of the nuclear family might be a good one, increases in numbers of divorces and separations of parents mean that many children do not enjoy the advantages that membership of a nuclear family confers on the majority.
Alternatives
An experiment to abolish the nuclear family occurred in Stalinist Russia — where the nuclear family was for a while declared an outlawed bourgeois institution. This resulted in so many abandoned children that the policy was quietly dropped. The kibbutz experiment in Israel, at its outset, attempted to ensure that children were brought up communally, i.e. not in nuclear family units. This had the unexpected side-effect that children of the kibbutz all tended to treat each other as siblings, and not as potential partners, as they grew up. They therefore sought partners outside of the kibbutz and tended to leave to form nuclear families of their own. The kibbutz therefore failed as a social experiment in this respect because it was not self-perpetuating.