This research design would best be classified as "Experimental Research Design".
Explanation:
Experimental Research Design is a model for scientific research that explores observations under controlled conditions. This means analyzing influence of independent variable on dependent variable, where independent variable is manipulated by interventional therapy and the effect on dependent variable of those treatments is observed.
Experimental Research Development is to determine whether classical music enhances the imagination of children. As: Independent variable — classical music is given in a controlled environment and its effect on Dependent Variable — Imagination test is observed.