Although "dialogue" is not really the right word, since that implies two people who are listening to one another speak and responding appropriately. Small children will sometimes listen to one another, but their responses are not always appropriate to the subject at hand.
The following, uh, talking activity occurred this morning between Cubby and a five-year-old boy at the library story hour:
Cubby: Come ride on my train! (His train is a long, cushioned window seat in the library.)
Other boy: Once we rode on a plane to visit my grandfather his name is Poppa well he has two names we call him Poppa but his other name is Ron* . . .
Cubby: I went on a walk with the dogs and a nettle stung me!
Other boy: I have another grandfather and he has two names too we call him Grandpa and . . . I can't remember his other name . . .
Cubby: This is the bed on my train!
It went on like that for some minutes. Neither boy was bothered in the least by the fact that the other child was talking about a completely different subject.
It exhausted me, however, trying to frame an appropriate response to two parallel conversations that had no intersections whatsoever.
It was very amusing, though.
* The lack of punctuation is a deliberate attempt to visually re-create the non-stop, no-pause conversational style of a five-year-old.