They were playing slaves and masters, and he was the master, and she was the slave. So, he's imagining their future and talking about it with Magda when they're older.

他们在扮演奴隶和主人，他是主人，她是奴隶，他正在想象他们的未来,当他们老了的时候他会跟Magda谈起今天的事。

耶鲁公开课 - 1945年后的美国小说课程节选