Water play

Incorporate water outside of just bathing. In the shower, direct the spray to different body parts (a handheld showerhead becomes a great stimulation tool for clitoris or penis). Try alternating warm and cooler water. Or use a wet washcloth stroked along the skin as a different sensation (warm, dripping water following it). Wet vs. dry: run a wet finger and a dry finger in parallel lines down their back so they can compare the feelings.