I don't have kids, but I have had a lot of losses. I would say if you are going, there are some events that the children would be fine at, and bring a welcome light to dark moods. waiting along the processional road is one, but perhaps not the viewing.
Let them be happy, don't fight them to be somber when they just can't be... The only time I was upset about children at my mother's service was the unfairness of expectation and harshness in some parents. The parents were stressed, I forgive them, but the parent was a bigger interruption than the laughing and playing of a child, if that makes sense..
I was 5 years old...and my mother had me watch the funeral and to this day I actually remember my mother crying when John John saluted the coffin...I remember it as clear as it happened yesterday...I wasn't too sure about the actual event I was watching...just remembered that little boy triggered my mother's crying...
That was our thought as well. Even the 3-yr-old can wave the flag -- our local Mem Day parade showed that!