Might I refer you to the Children Act 2004....
You may think your choices are perfectly fine - but according to the above act, and a myriad of other Safeguarding Children legislation they are not fine - they are far enough from fine to be considered a Safeguarding issue. You are placing your children "at RISK of emotional harm". That's all it takes to be in breach of the law. You don't have to cause actual harm - just behave in a way which MAY cause harm.... which you are doing.
If you don't watch things first you have no way of knowing whether or not they might be worried or frightened by what they see - so by allowing them to watch without checking first you are placing them "at risk of emotional harm". The ratings are there to tell you whether something has the potential or is highly likely to cause emotional harm to someone below the age specified. It's one thing to ignore it - it's another to not even check first.
So you are clearly placing them "at risk" - and should they be scared or worried or desensitised then you have actually caused emotional HARM. Obviously if they are scared/worried/uncomfortable enough to "leave the room" then they HAVE been subjected to emotional harm - because leaving is a reaction to what you have allowed them to see, and a reaction has a cause...
Many children who are exposed to inappropriate material do not demonstrate behavioural issues until long after the fact, and it's only through psychological help that the cause becomes apparent.
You're storing up potential mental health time bombs for your children by letting them have access to material they are emotionally incapable of processing. They can be as intelligent as you like, but you cannot speed up emotional maturity.
But then if the balloon does burst in your face and one another of your children develops a mental health issue will you also then be saying it's not your fault as per your daughter's anorexia??? Probably.
There is a saying... "Parents...they fuck you up". Sounds like you're doing a grand job on your children.
Shoddy parenting, very very shoddy.