**Study Overview:** This study is testing a medicine called *patiromer* for children under 12 with *hyperkalaemia*. Hyperkalaemia is a condition where you have too much potassium in your blood, which can be dangerous. This study checks how well the medicine works, how safe it is, and how the body handles it. **Eligibility:** Kids in the study must be under 12 and have high potassium levels. They need to be able to take medicine and food through regular or tube feeding. Certain medicines should be stable before joining. Some children can't join, like those with certain kidney problems or recent cancer treatments. **Key Points:** - **Study Duration:** The study lasts for 28 days. - **Visits:** Participants will need to visit the study site regularly for check-ups. - **Risks and Safety:** Check if your child has any of the exclusion conditions like certain kidney issues or medicine allergies. Parents or guardians must be involved to ensure children attend visits and follow study procedures. This study aims to help find safe treatments for young patients with high potassium levels.