Child abuse & neglect..... how much say do we have?

I recently had a horrible experience/ encounter with a family on a train which to my horror i had no control or say over....it happened a couple of weeks ago and i was with my family on our way back from a trip. We were sat in front of a family that had a few kids not sure exactly how many at least 3 we could see anyway and a young boy probably the same age of mine so roughly 3 plus. He was continually smacked and slapped and pulled by his clothes by the father, grandmother and possibly mother we couldn't see it all but heard every last one of his torments. The poor boy wasn't even doing anything out of the ordinary that any normal 3 year old would do he certainly wasn't being naughty and definitely didn't deserve to be treated in this way. The boy tried to interact with my children over the seat but was pulled back to be tormented by his dad and he actually said i could hear clear as day"look at you you scruffy snotty little tramp your disgusting" to this i stood up and had to control my almost outburst i felt like saying to him well take a look at yourself!.....i was so angry :0( earlier on i could hear the little boy say "no one looks after me no one cares for me" i could have cried. Its so saddening that i had no control over the situation and had to sit back down as if i had of said something then i could have been abused by the father and the little boy certainly would have got another good hiding from the reaction. It sickens me to think if they do this in broad day light then what happens behind closed doors? I have been given a book  which i read parts of whilst travelling but had to put down a few times it's called " A Child Called It" by Dave Pelzer a true story about a boy who took a remarkable journey through a life of abuse by his mother, thought it might come in useful for discussion in child protection/safeguarding module.