Delayed Gratification: M&Ms

In this experiment, researchers test the impulse control of children. An experimenter tells the children that if they wait to eat the candy they will receive four more M&Ms.

The experimenter leaves the room to observe the childrens actions through a two-way mirror. What was the research question in this experiment? What types of data could the researchers collect from this research method? What type of research is this considered? Do you anticipate any limitations from this research?