These exchanges have no content in the adult sense, but meaning exists nonetheless. There is you, and there is me. Instead of an object, an event or happening could capture the child's attention. But the outcome is the same. The characteristics of a conversation, including intonation and turn taking, are present.
Meaning is created at the point of impact.
In Hallidays's scenario which follows, the mother is holding the baby in her lap and throwing and catching a toy rabbit while the child watches attentively. No, that's enough. Let's find something else to do. As the child grows and begins making more intelligible utterances, the mother transfers more of the responsibility for continuing the dialogue to the child. The dialoguing ritual provides for optimal learning as the caregiver continues to model the language and support meaning making.