Rafael Cabral scored a hat-trick for Portugal before Ronaldo Jr came off the bench.
Ronaldo Sr, 40, has scored 136 goals for Portugal, a record in men’s football.
He captained Portugal to their first major title at Euro 2016 and the Nations League title in 2019.
Ronaldo Jr is at Al-Nassr in Saudi Arabia with his father, who signed for the Pro League club in 2022.
Ronaldo Sr forward has four other children – twins Eva and Mateo, 7, Alana Martina, 7, and Bella, 3.
Portugal U15s are playing at the Vlatko Markovic tournament, where they will face Greece on Wednesday and England on Friday.