To grow that perfectly round, toned butt without growing your legs, you should add exercises to your workout program that activate your glutes as much as possible while activating your legs as little as possible. Make sure you keep getting stronger during the glute exercises by adding weight or by increasing the number or reps or sets, because this is the stimulus your butt needs to grow. So work your ass off to get that round butt that you have always dreamed of!
The gluteus muscles are used for stretching and rotating your hips. They also help to move your legs away from or toward the center of your body, movements that are also used during leg and glute exercises. Think of squats, lunges and romanian deadlifts, exercises which are known and widely used as butt-shaping exercises. However, what these exercises have in common is that the focus of these exercises is primarily on the quadriceps and hamstrings. By doing these exercises, you do not only stimulate your buttocks to grow, but also your legs.