This study, titled The BONEBRIDGE in Children Under Five: Premarket Clinical Investigation (Study ID 2023BB006), looks at kids under five who have received the BONEBRIDGE BCI 602 hearing implant. This observational study, which is both retrospective (looking back) and prospective (looking forward), will take place at multiple hospitals. The main goal is to see if the BONEBRIDGE implant is safe for young children within 12 months after surgery. Primary Goal: The study's main aim is to collect all information about any bad experiences or issues related to the device and the surgery to check its safety. Secondary Goals: Hearing Improvement: Using tests like the Göttinger Speech Intelligibility Test (Word Recognition Scores) to see how much the hearing improves with the implant. Treatment History: Surgeons will fill out questionnaires about how the treatment went. Quality of Life: Parents will answer questions about their child's quality of life using the GCBI questionnaire at least 12 months after the implant. The study will last up to 12 months, including enrolling participants and performing all necessary procedures. The target number of participants includes at least 12 sets of data for safety checks and at least 5 sets of hearing performance data. By collecting detailed information on any problems and assessing the performance of the BONEBRIDGE implant, this study aims to determine if it is safe and effective for young children.