Hebrew education?

This Shabbos, after lunch, as PJ was going up for his nap...

PJ: "Abba, I want to go to Areilla's house to play after my nap."

Abba: "We'll see."

PJ: "You should talk about it with Mommy in Hebrew now."

We use Hebrew to talk about things we don't want him understanding. We sort of know that at some point he may start to learn it- now we know that he knows what we are doing, though I can only guess how much of it he does understands.