Most people care about other people. Most people would report something if they for a minute thought that a child was being starved. The reality is that they aren't things you would think someone was doing. I like Boo have a skinny child, he's also an escape artist, hes also always hurting himself, I could easily be at the end of an accusation. People know me though, and know I love my children but I suppose if I went through a mental episode and did something horrendous people might still not suspect me of foul play.
I think the big issue is, since that little girl in London was murdered by her aunt a few years ago, there has been a new chain of communication. You sign forms when your kids start school or nursery to make you aware of this, if your kid gets hurt, turns up with bruises, this can be shared with your doctor and social services. Same goes for if you don't send your kids to school. I would think this poor little girl's school is going to have to answer some questions.
I have phoned social services on one occasion. I got the police involved first and they told me to phone them, they showed up that night and removed the children from her care.