Brianna and Grayson each have a bucket of blocks and each is building a tower with the blocks on the floor. Brianna runs out of square shapes and sees that Grayson has some left. She asks Grayson for one, offering to trade a triangle in return. Grayson makes the trade and asks Brianna is she will trade another triangle for a square. Brianna and Grayson are engaged in:

associative play.

Explanation:

Associative play: The term "associative play" is described as a phenomenon that includes the "social play development" through children or preschoolers. Associative play is considered as the very first stage in which a child interacts socially and is often considered as important in children's play because they've started engaging in mutual activities yet not demonstrate a common goal.

The most common age in which a child is engaged in associative play is three to four years of age.