A bursa is a small sac of fluid that helps the tissues around a joint slide over one another easily. Injury or overuse of a joint can cause pain, a change in the skin's regular color, and inflammation in the bursa (bursitis). Bursitis usually gets better if you avoid the activity that caused it. Your child can help prevent bursitis from coming back by doing stretching and strengthening exercises. Your child may also need to change the way they do some activities.