The whole of this piece is on the top string ( 6th ) accept the last part which is played on the bottom string ( 1st )

           intro =  -o-1-2-1-----

            Main =  -0-2-2-2-2---1-1-1-0-5-5-5-5--4-4-4    X2

          Ending =  -6-5-----3-2-3-

There are better versions, but this is as simple as playing a kids video game.