Adults call this "The Spark." Children call it "Resource Evaluation."
Children are far more observant than adults often give them credit for. Long before they experience romantic love firsthand, small children (typically ages 3-8) are absorbing, interpreting, and mimicking the relationships they see around them. Their understanding of romantic storylines is a fascinating blend of literal observation, fairy tale logic, and emotional processing.
Around ages six and seven, the "cootie" phenomenon often takes over. This is a crucial developmental stage where children begin to form stronger gender identities and peer groups.