Why do people discourage future aspirations of kids who have similar talents to them? If your kids have musical talent, give them opportunities to learn, to master their instrument of choice including their voices. 

I had parents who restricted choices that frankly had longterm consequences for my siblings. 

Anne's 3 year old grandchild needs to know that if she wants to sing, that's awesome and may her parents support her along the way. Anne's experiences, positive and negative, are hers alone. That doesn't mean they'll be replicated by others.