The answer is "Onlooker Play".
Mildred Parten Newhall was an American sociologist who presented the theory “stages of play” in 1929. In the case above mentioned the “Onlooker play” means that children see other mates playing but do not directly involve in that though he/she may engage in other kind of interactions about that for example talking about that or in the above case mimicking about what he sees. According to Parten there are six various kinds of play.