English or Nihongo?

After we got back from Japan, Tesshin has been trying to speak a lot more. He doesn't say words but his sounds are more diverse now. He can also respond to me whenever I speak to him in Japanese. After I pick him up from daycare, I'll let him roam around in the front yard. When I get tired of chasing after him, I'll say "Let's go inside the house" or "C'mon Tesshin, let's go". He'll turn the opposite way and walk away from me (with a huge grin on his face). But if I say it in Japanese "Tesshin, oide or Tesshin, ikuyo" he'll turn around and come towards me and follow me into the house. Same with asking please. If he's holding the remote in his hand "I'll say "Tesshin can I have the remote, please" Nothing. Then I'll say, "Tesshin, remote choudai". And he'll give hand it over. I'm very encouraged that he's learning key phrases in Japanese since my parents don't really speak English. I always worry that they won't be able to communicate. Yukiko-san gave me some books for Tesshin "The Very Hungry Catepillar" and "Curious George" but they're written in Japanese. I guess I'll be learning Japanese too.