Simplify the following text for a Grade 7 native English-speaking person.
Original: Sirenomelia , also called `` mermaid syndrome '' , is a rare congenital disorder in which a child is born with his or her legs fused together and reduced genitalia .
Simplified: Sirenomelia , also called `` mermaid syndrome '' , is a rare disorder . It happens when a child is born with his or her legs grown together and little or no genitalia .