My? Whomever the heart belongs to. Adults can have their hearts broken but I speak mostly of the hearts that belong to children. Every child has a special love of something in his heart. If that something is taken away then that child's heart will be broken. Adults, whether parents, grandparents or teachers, are usually the ones who break a child's heart. Usually the adult will take away "that thing" to punish the child for a misdeed, but that is never the proper thing to do. There are many other punishments that may be meted out that will get the point across and help to make the child behave. But if you take away that "one thing" the child may never reach his full potential or be as happy as he would have been.
One man I personally knew always wanted to play football. Although he became famous in his state as a basketball player his true passion was football. As his mother thought that the sport was too dangerous she never let him play football. He eventually became an alcoholic, was arrested for DUI many times, besides other problems in his marriage. Can playing football be dangerous? Of course, but would it have been more dangerous than ruining his life?
It's not only an activity or an inanimate object but also inattention, isolation or ridicule can break a child's heart. Special needs children are more prone to have their hearts broken as they don't understand all that is happening to them. The more vulnerable the easier their hearts are broken. Supervisory adults should be extra sensitive in this area so not to totally destroy their wards. We adults will eventually die but what kind of child do you want to be left behind? One that was well nurtured or one whose heart you broke?