What’s a Nuclear Family? And Who’s Included in One?


Family is one of those terms that is easy to define in its generalities. This is when it simply means people who are related to each other through a blood bond or a connection because of someone’s marriage. In the end, the definition of close or ‘distant’ a particular family member is far more complicated.

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For instance, the term "nuclear family" is used to refer to the most core unit of society, like the nucleus of a cell. In many cases, the households that people in the United States inhabit simply don’t look anything like a traditional nuclear family.

Who is in your family may seem obvious, but every culture defines the connections of family a little differently. Here are some important things to know about the history and implications of “nuclear family” as a concept. These factors are particularly as applied in the United States, and don't apply to every culture within or outside the U.S.

Nuclear Family Definition

The general definition of a nuclear family is two parents and their children. Children are included only while they’re young enough to live with their parents.

This family unit became widely recognized because it’s where many of society’s rules and norms are passed along from parent to child. Sociologists see the concept of a nuclear family as a fundamental building block of society.

A nuclear family is not solely defined by these people living together under one roof. That being said, the word carries some baggage as a "traditional" concept of what defines a family. It implies a mother-father pair with their children, all living together.

There is a period of time when children are not living at home but haven’t created their own nuclear families yet. It tends to be a time when they can be treated as part of their childhood nuclear family. They’re also considered adults outside of the nuclear family framework at certain points.

In modern society, second or third marriages are very common. That means there could be a better, more expansive definition: “a parent, that parent’s partner, and the children that live with them.” Depending on the context, children may live with that couple full-time or part-time.

Also, a parent without a partner would also be the head of his or her own nuclear family. Such a nuclear family would include them and the children that live in their home.

Nuclear family example

One example of a nuclear family would be Lois and her husband Mark, with their three children Jen, Parker, and Sam. Their cousins, aunts, uncles, and grandparents would not be included.

Jen, Parker, and Sam would ‘exit’ the nuclear family when they become adults. At that point, they’d form nuclear families of their own when they choose partners and begin to have their own children.

If Lois was living with her second husband Stephen instead of Mark, and Jen, Parker, and Sam lived with Lois and Stephen full-time, that’d also be an example of a nuclear family.

If, between those marriages, Lois had full custody of the three children, the four of them would also, at that time, be considered a nuclear family.

Difference Between Nuclear, Immediate, and Extended Families

Nuclear families, as we mentioned, focus on the parents/partners and children when they are of an age to still live with their parents. Immediate family often includes these same people, but it also focuses on people who are closest to you on a family tree.

Your own parents, your own spouse, and your own children would be considered then as your immediate family. The child of your sibling would not be an immediate family member. Also, your own grandparents wouldn’t be immediate family, since they aren’t ‘directly linked’ to you in the same way.

Some fuzziness can exist in the definition of immediate family. For example, grandparents raising their grandchildren might be also be considered immediate family.

Immediate family members can include step-parents and step-siblings in blended families. If a child lives with his or her step-parent and step-siblings, they’re all part of a nuclear family.

Many of these ‘non-immediate’ family members fall into the category of extended family.

“Extended family” takes into account almost anyone who can trace a shared ancestor with you. Because of this, a second or third cousin is just as much part of your extended family as your own grandparents or grandchildren. Extended family can also include people only related to you by marriage.

Extended is generally juxtaposed to immediate family, but it can also sometimes be used to contrast with your nuclear family.

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Who’s Included in Your Nuclear Family?

While every nuclear family is different, this tends to be the group of people who are included in a nuclear family.

  • Mother
  • Father
  • Brother
  • Sister

One additional area would be in blended families. The nuclear unit could be one parent and one step-parent, as well as any siblings and step-siblings that live together.

In some families, long-term foster placements also become part of the family unit, making them members of the nuclear family. Such a unit, in being in the same household and growing up together, function in basically the same way as a traditional “nuclear” family.

Who Isn’t Part of Your Nuclear Family?

Your extended family tends to be everyone related by blood or marriage who aren’t part of a nuclear family. As families change, there are more people who have extended family members living with them in their household. Still, based on the traditional definition of nuclear family, these people wouldn’t be included in the nuclear family.

  • Grandparents
  • Aunts and uncles
  • Cousins
  • Half-siblings, especially those who don’t live with you.
  • Nieces and nephews
  • Ex-spouses are usually considered not part of the nuclear family

Importance of Nuclear Family Definition in Work Policies

Many companies will make their allowances for bereavement travel and time off based on a particular definition of “immediate family.” Most of us aren’t expected to only restrict our grief to members of our nuclear family, which rarely has more than a few people in it.

As an adult, for example, your parents aren’t usually part of your nuclear family anymore. After all, they live elsewhere and you’ve formed a unit with your own spouse and children.

If your company has chosen to define their bereavement leave policies as applying for only one’s nuclear family, encourage them to shift this policy. The definition of a nuclear family no longer applies to a majority of family units. Also, many adult daughters and sons are more likely to participate in planning funeral arrangements for parents or grandparents.

You may wish to attend a funeral or plan one for a family member who is outside of your nuclear or immediate family. Even if you can't get time off, you should still be able to find a way to participate and remember them.

If you absolutely cannot get time off on the day of the wake or the funeral, consider whether or not you can visit the gravesite personally during your off days. You might also organize a future memorial service. More family members who couldn’t arrange their schedules quickly to attend the funeral will be able to mark their calendars.

Understanding the Nuclear Family

While there are still many family units that include a mother, a father, and a few children, not every family unit can be described by the old definition of a nuclear family.

Much of the closeness, cohabitation, and reliable parenting is now coming from outside traditional nuclear families. Close family units now include single parents, blended families, and same-sex couples raising children together.

While these do not fall into the category of ‘nuclear’ family based on definitions from decades ago, they meet the general metric of being the live-in family members who parent, love, and support the children growing up in their home.

When you are planning a bigger event, like a family reunion, the distinctions between nuclear and extended family fall away. The goal is for everyone to focus on being close and caring for each other, rather than how far apart they are on a family tree.


  1. “The Evolution of American Family Structure.” Family Sciences Department. Concordia University Saint Paul. online.csp.edu/blog/family-science/the-evolution-of-american-family-structure
  2. “Family and Medical Leave Act.” U.S. Department of Labor. dol.gov/agencies/whd/fmla

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