I'm with the 'safeguarding is everyone's responsibility' camp.
The way it works in jobs where people actually understand safeguarding is that:
You have a concern - however small
You report it to someone whose job it is to respond
They respond
Sometimes it is acted upon, sometimes, it just gets reported because it might be an isolated incident of something that isn't great, sometimes it might be a piece in a bigger picture that adds to it
Sometimes, it's a clear cut case of abuse - e.g. mummy put the iron on my leg because I was naughty - and the reaction is immediate.
Often, it's a slow building picture of neglect that is pieced together.
Those saying the OP doesn't have any idea of the circumstances or whether there is any other issue going on are quite correct but that's the point, she isn't expected to conduct a full investigation herself, she can just let someone know that she's concerned.
The Local Authority child protection database is full of stuff like this that are either never acted upon directly; or cases are closed because it was an overzealous report by a neighbour or a malicious report by an ex. And they are also full of slow building pictures of abuse.
That's all the OP would be doing - not making a decision herself but letting someone know who might well be aware of a bigger picture.