Starry-Sky Projection and Maternal Voice for Sleep After Pediatric Cardiac Surgery

The goal of this clinical trial is to determine whether a starry-sky projection affects sleep during the early period after cardiac surgery in young children. The main question it aims to answer is: • Does a starry-sky projection improve how well children sleep during the first three nights after surgery compared with routine nighttime lighting? The study will also explore whether sleep outcomes differ between children who listen to their mother's recorded voice and those who listen to an unfamiliar woman's recorded voice, and whether the effect of the starry-sky projection differs depending on the type of voice. Children aged 6 months to 6 years will be randomly assigned to one of four combinations of visual and sound conditions. They will: * Receive either a starry-sky projection or routine nighttime lighting * Listen to either their mother's recorded voice or an unfamiliar woman's recorded voice * Have their sleep monitored during the first three nights after surgery using a contactless device placed under the pillow that does not require sensors attached to the child.