[Rive1976]

If a 5 or 6 year old is touched by a 8 or 9 year old is it sexual abuse or does it have to be a 5 year difference?

[Amyjay]

My thoughts:
From the point of view of experience - the 5 or 6 year old may or may not experience that as a traumatic/abusive event. That would depend on the how the 8 or 9 year old acted - aggressively? Out of curiosity? Forcefully? Playfully? and other factors too most likely. Children touching themselves and each other is very much a normal - though not universal - experience of childhood.

From the point of view of experience - the 8 or 9 year old may be acting out of normal childhood curiosity about sex or be acting out his or her own abuse or be acting with an intent to harm.

If the older child was acting out own abuse or with intent to harm that would be a red flag that the child needs intervention, help and support.

There doesn't have to be a five year old gap for the event to be experienced as abusive for the younger child. Human experience doesn't care about a predefined legal definiton.

The older child is not criminally /legally/ morally accountable for his or her actions, no matter what. The older child is still very much a young child.