When is a parent classed as failing to protect their child or children? or the person who saw something happen in the street to a child or children, classed has failing to protect , because they never said anything at the time?

Something that you see has innocent !, -E.G- Children playing in the street a child trips and falls over, a man walking past sees this, goes over to pick the child up, make sure that child is alright, you are walking a little behind see this happen, do not question him, The man sees you have seen him help the child, You say nothing to the man or the children, carry on  past, after all he has gone over to see if that child is alright, no need for you to stop right?, no need for you to say anything, all looks innocently done,  the man carries on with what he was doing before he helped the child, no harm has been done to the child via what you saw with your own eyes, right ?....

But what if that scenario was different?!...What if something you saw has innocent, ...( i.e- the man helping the child, and then walking on) A few days later even months later, that child says what you saw happen but adds on the end something totally different to what you saw, when the rest of the children are asked  all the children agree with it, then later on, that child goes on to change it back to what you originally saw and again all children agree!....

 Do you believe the child/children and  report what the child has said, even though they changed it back later on? , That child  could be telling the truth right? and has just said it to you, so what if that child was to say it to someone else?.... Another question.... what are you actually reporting???

 It could be that that child is just saying it! Did that child realize after saying the bad story  that that was a lie, so then changed it back at which point the rest of the children realized they should to, Do you has a parent or just a person report it on the basis of, What if that child is telling the truth, even though what you yourself saw with your own eyes was innocent!,

 The problem is you do not know 100% in your own mind,.... because you carried on walking !!

In today's world  where the Authorities aim in the UK is to go at everything like a bull in a china shop and ask questions 6 months later, especially when it comes to children!!...How do you differentiate  what you see has innocently done with, or towards a child, from failing to protect because you has a parent or as just a person, never reported it at the time it happened?

How in today's world do you differentiate what is innocently done via a man,  from the possibility of,  if that man had not seen that you had seen him  he could of done  something to that child or children then or at a later date??