Most kids enjoy each other’s company in the tub and playing together. Just like with my kids, eventually, the fun stops. One wants to play boats and trucks in the tub the other wants to play Barbies and beauty salon.
There is no definitive rule as to when shared bath time should end. Go with your instincts. So long as your children are happy and comfortable, that’s what matters. As soon as they begin fighting, ask for privacy or become embarrassed, it’s time to respect those wishes and separate the kids.