
Italophilia:
he started learning Japanese on his own using Duolingo
Anch'io! I'm also a language buff and also an Italophile. (Living in the middle of Europe makes both of these far more practical for me than you. I can even drive to Italy - albeit a long drive.)
I don't want to get too off-topic in this forum, but I just want to say that I'm also a committed Duolinguist. I know you're already using Pimsleur, which has a lot of strengths, but there are some very good things about Duolingo: it's fun, the lessons are short enough to be easy in one's daily routine, and they offer a really broad range of languages - and if one pays for premium (which I do), you get all of the languages for that price, so it's quite worthwhile for polyglot language buffs. Moreover, I find it really great that I can (for the same price) do language combinations like "French for Italian speakers" or "Chinese for Japanese speakers", which can be a bit immersive (and fun!).
On the minus side, Duolingo doesn't do a good job of teaching grammar or conversation, so it's better for refreshing or building upon some existing knowledge. Also, it has Vietnamese, and even Cantonese for Mandarin speakers, but not Thai - grrr!
Anyways, here's what I wanted to say (regarding your son): Although Duolingo free is very usable, it's so much more engaging and satisfying in the premium "Super Duolingo" version - and here's what I really want to say: they offer an annual "family plan" that doesn't cost much more, so you could buy it for your son, yourself and up to four others.
P.S. In addition to English for Tagalog speakers, it also has French, Italian and Spanish for Tagalog speakers!
P.P.S. I see that Pimsleur has Thai, so maybe this should be my excuse to try Pimsleur. (Such a disgrace that I'm not fluent, despite having watched 1000+ hours of Thai BLs.)