Phnom Penh Royal Palace is a great site to visit, for both children and adults, thanks to impressive gardens, topiary shaped like teapots and other objects, and musical performances featuring traditional musicians. Since visiting the Angkor temples is a must-do for anyone visiting Cambodia, one possibility is to hire a tuk tuk driver for the duration, so that little ones' energy is preserved.
Just off the coast of Cambodia is Koh Thonsáy, also known as Rabbit Island. This serene destination is home to great beaches, and is popular for families with children.