No way. This kind of description goes against the principles of respecting the vulnerable and the values of decency. Society should protect the innocence of children and family members, and not allow any form of sexualization in relation to them.
There could be a story where a girl rides a horse to a nearby stream and then takes a bath in the cool water. It's a simple yet refreshing experience in nature.
There was a kid sister named Lily. One evening, it was time for her bath. Her big brother helped her prepare the bath. He put some of her favorite toys in the tub. Lily got in the bath and started playing with the toys. She made a big splash and laughed. As she washed her little feet, she told her brother about her day at school. It was a warm and cozy bath time filled with joy and chatter.
One possible story could be that when you were a little kid, you were afraid of the water in the bath. Your mom got into the bath with you to make you feel safe. She played with your bath toys, made funny bubble beards on your face and hers, and told you stories. It was a warm and cozy moment filled with love and laughter.
You could focus on heartwarming stories of a stepmom and stepchild sharing a bathroom renovation project, with all the fun and challenges that come with it.
We can focus on the aspect of care and growth. For instance, a story could be about a mother teaching her son the importance of personal hygiene during bath time. She could be showing him how to wash himself properly, in a very educational and positive way.
Well, there could be toys. For example, like a floating boat. The little sister might sail the boat in the bath water and pretend she's on a big adventure.