Place cookies in the bowl of a food processor; pulse until the consistency of fine crumbs. Set aside.
Step 2
Beat cream cheese, confectioners sugar, butter, and vanilla extract in a large bowl with an electric mixer on low speed until combined, then beat on medium speed until smooth. Add milk and pudding mix; beat on low speed until combined. Fold in whipped topping with a rubber spatula.
Step 3
Layer 1/3 cookie crumbs into an ungreased 9x13-inch baking pan; top with 1/2 pudding mixture, 1/3 more cookie crumbs, remaining 1/2 pudding mixture, and remaining 1/3 cookie crumbs.
Step 4
Tuck ends of gummi worms in cookie "dirt." Be sure to place a worm on each piece. Refrigerate before serving, at least 3 hours. Cut into 15 squares. (If serving in a clean flower pot or sand bucket, serve with a clean garden trowel or a toy sand shovel.) Store in the refrigerator.