Cousins are like the perfect blend of best friends and siblings. A fixture at family celebrations, holidays, special events, and important milestones, these relatives are an integral part of a child's upbringing. Kids may understand where they fit into the family tree, but there is so much more to learn about genetics, culture , and historical perspective on these relations. Be sure to add some of the best children's books about cousins to your child's collection!

Everything to Know About Cousin Relationships

• Marrying first cousins is illegal in only about half of the US states, but marrying second cousins is perfectly fine in the majority of states.

• Some of the states that allow the marriage of first cousins have certain stipulations in place. For instance, Indiana, Arizone and Illinois will only permit first cousin marriage if the woman is of a certain age or cannot have children of her own.

• A few states have passed laws making it completely illegal to marry cousins of any kind, no matter how distantly related. These states actually consider it a criminal offense. So, if you want to marry a cousin, definitely do not move to Texas, Nevada, North Dakota, South Dakota, or Oklahoma.

• If first cousins have a baby together, the risk of a birth defect doubles. But it is still a fairly low percentage (4%-6%).

• There is a holiday devoted to cousins. July 24th is the official National Cousins Day, so plan a party and invite all your cousins over to celebrate!

• First cousins share about 12.5% of their DNA. For comparison purposes, siblings share about 50% of their DNA.

• About 10% of marriages worldwide are between cousins.

• In the most basic sense, cousins are relatives who share common ancestors.

• First cousins are the offspring of siblings. 

• All Europeans of Jewish descent are distant cousins.

• An interesting study indicates that third cousins who marry and decide to start families experience higher rates of fertility compared to the general population.

• There are so many versions  depending on how closely related they are to each other. First cousins, second cousins, and cousins once removed are just some of the ways to define the relationships. However, there is another, less well-known version called double cousins. If two brothers marry two sisters, their offspring are considered double first cousins!

• The blood relationship between cousins is equal to that of half siblings.

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