After the failed extraction of information from Saito, Cobb claims that he's "getting off at Kyoto" and we later see him in a hotel room. He spins his totem--the top--to make sure he isn't dreaming, and then receives a call from his children.
How do they know where he's staying? As his father-in-law (Michael Caine) later says,
It'll take more than the occasional stuffed animal to convince these children they still have a father.
So we know he isn't in contact with them a lot. Additionally, he wouldn't want to risk making a call to the United States where he is still wanted for murdering his wife.