It's too traumatic, they're disruptive, they won't understand, we need to protect them from the reality of death, they'll be emotionally scarred...
The reasons for excluding children, from what is essentially a major family occasion, are many and in my opinion, unfounded.
The passing of a loved one is of course a difficult subject to address with a child, especially true if the death is unexpected or the circumstances are unnatural, but being involved can prepare children in a positive way for the time when they lose those closest to them and enable them to deal with their emotions in a positive and supported way.
When my Grandad died last month, we sat our 6 year old down to tell her the news. She had visited him in hospital the month before and was understandably upset, albeit in a quiet way. We answered all of her questions honestly and used simple language (with no mention of angels or heaven) and she was keen to know more about what happened next. After explaining what a funeral was (a chance to say goodbye, give thanks, be with family who would be feeling the same way as we did) she expressed a wish to go but of course the decision was not ours to make. Children were excluded and our 6 year old was in tears. Her argument, and she did argue her point, was why wasn't she allowed to say goodbye when grown-ups were. I couldn't disagree with her that this was a valid point and my concern is this: by excluding children from what is a very normal part of life, do we risk instilling in them feelings of resentment and anger in later life?
I'm not in any way saying that children should be forced to attend funerals, it's important that they understand what will happen and can make an informed decision, and this will depend on the maturity, not the age, of the child. But if they do wish to go, there's plenty of information available to help families prepare them for the experience.
During the run up to our family funeral I read lots of articles and research on taking children to funerals but the paper 'My Grandad plants people!' from the Bereavement Advice Centre sums it up perfectly. With advice on how to explain death, what happens to a body when they die and what funerals are for, it contains most things a parent or guardian could need to discuss death with a child.
I still believe my daughter would have benefited from being able to say goodbye to her Great-Grandad, because after all what is the alternative; what is she left with? Basically he was here, but now he's not. He's simply disappeared.