Well, it does happen in families. If the children are old enough, they'll want to know what happened to their brother or sister. There's a way to explain it age-appropriately, just like explaining other aspects of reproduction.
I've had two miscarriages, so I understand the concept ... but it seems to me that if children are old enough to realize their mother is expecting a baby (and not just fat, as my 5-year-old kindly mentioned to me a couple of months ago), then they're old enough for a simple, verbal explanation of pregnancy loss from their parents.
Just my own opinion, of course, but if one of my church ladies mentioned a children's book on miscarriage to me, I'd think she needed to work through her own grief with a good Christian counselor, not project it onto young children.