neighbor mows her lawn on a rider mower with baby on her back is this child abuse under WA law and should it be reported

When I was in the Peace Corps in West Africa, the local women tied their young children to the women's bodies and went about their work.

I have read studies whose conclusion is that babies who are held close like in Africa are more emotionally bonded with the persons holding them.

So, is what you observing abuse? Offhand, I cannot say for sure. It likely is not the neighbor's intent to be harming the child.

Are you in a position to have a chat with the neighbor? Or have another neighbor have a chat with the neighbor?

Keep in mind the the government sometimes overreacts (and sometimes underreacts). If you feel the child is in danger, you can call the police or Child Protective Services.

If in doubt you can report it to CPS or whatever Child Welfare is called in Wisconsin. All states have laws that keep child abuse reporters' names confidential. If CPS then thought it was a problem, they would go have a chat with your neighbor. So why not let the experts handle it?