Remarkable that your son can sound like a native in two other languages, in addition to his native English.
I've met several people who have been able to cross into native-sounding territory after learning Spanish as adults.
A former co-worker, caucasian from East Texas, developed an interest in Spanish after visiting Mexico with his church when he was about 18. Today, he has a hard time convincing people he's NOT Mexican.
He once told me he has a harder time preparing an English sermon, preferring to do it in Spanish.
He's so good that he's bad, having mastered all the bad habits: <<Oiga, José, mi compu no jala, y no sé qué le pasó, pues no se me ha cáido>>.
compu: computadora (laptop); jala: no funciona (inoperative); cáido: caído (haven't dropped it).
Cáido, with emphasis on the first vowel is obviously wrong, but this guy knows it, and depending on his audience, he can navigate in and out flawlessly.
He's probably the fastest English-Spanish translator I've ever met. And he's now translating Hebrew into Spanish for his church.
I met a speech therapist, African American, whom I mistook for Colombian from Buenaventura, who could speak 5 languages.
Her command of Spanish was incredible, but she assured me her Portuguese and French were even more fluid.