Gradma showering with 7yogirl and 9yo boy?

During a custody dispute, between the grandmother and my sister in law, a grandmother to my niece and nephew was showering with the children, separately. My niece brought this up with me today and told me how they discussed grandma's and pubic hair (that's all the info she gave) The grandmas son (biological father) is a convicted child molester (not of these children.) I plan on reporting this incident for piece of mind if nothing else but are their laws against this? Indecent exposure, ual abuse ? Being a weirdo? I know i need to tell a police officer and have their mother tell their counselors. But in WA does this break any laws.