This is a normal occurrence and is usually only temporary. Parents should address the situation in a way that doesn't turn into a battle by forcing their child to practice. Make music lessons and practice time a high priority. For a child studying music, having too many extra-curricular activities can interfere with the development of productive practice habits.
Communication is key.
Discuss with your child's music teacher his or her philosophy of practicing and what will be expected of your child on a weekly basis. Then, parents and student together can decide on a daily schedule that will be used exclusively for instrument practice and to complete the teacher's lesson assignments. Providing a room in the home free of distractions during the daily practice time is essential. Accomplishing mutually established practice goals is more beneficial than practicing for a specific amount of time. Don't force your child to practice.