What is the name of song that Selena Quintanilla sang in movie when little with dad?

The movie you are referring to is likely "Selena," the 1997 biographical film about the life of Selena Quintanilla-Pérez. In the movie, young Selena is played by actress Jennifer Lopez. In one scene, young Selena performs the song "Papa Quiero Ser Cantante" (Daddy I Want to be a Singer) by Marta Sánchez on stage with her father, Abraham Quintanilla. The song becomes her first hit.