Childhood Friends Romance

"Zazu: Oh, just look at you two! Little seeds of romance blossoming on the savanna. Your parents will be thrilled, what with your being betrothed and all. Simba: Be-what? Zazu: Betrothed. Intended. Affianced. Nala: ... Meaning? Zazu: One day you two are going to be married! Simba: Yuck! Nala: Ew! Simba: I can't marry her, she's my friend! Nala: Yeah, it'd be so weird."

- — The Lion King

Childhood Friend Romance is a part of romantic plots, when characters develop romantic feelings for someone who they spent their childhood years with.

In the cases when this love turns out to be one-sided, it is sometimes explained with "Westermarck effect", a theory that claims that people who grow up together are psychologically hardwired to think about each other Like Brother and Sister.

This theory was later questioned when it was realized that though few of the people studied had major romantic relationships with childhood friends, many had crushes and romantic feelings that just didn't make it.

When it is mutual, and none of the characters are bound by the "Westermarck effect" (maybe because they only met when they were older than 6, when it's supposed to apply, or only for a shorter time), it is usually played as a special bond between the two characters.

When it is one-sided, the friend might grow to care for the other's child or sibling.

The victorious form can be a Second Love, after one or both have married, and then lost their spouses

See also I Don't Want to Ruin Our Friendship which these kind of romances may be postponed or avoided because of a strong childhood friendship or Just Friends or More than Just friends?