Update after added info above. Without knowing much about your team, my advice is this. The request from your manager should be taken as optional. Unless it's

Update after added info above. Without knowing much about your team, my advice is this. The request from your manager should be taken as optional. Unless it's part of your contract explicitly, it's really the manager's job to oversee and coach the juniors on the team. Don't accept it as part of your job because it will slow you down. You already mentioned you are having difficulty with efficiency. Instead, create a better learning environment within the team. If there's not already a code review process on your team, start one. Encourage them to pair with each other more than with you. If you like teaching and giving workshops, keep doing that, but go public with it and do it outside work hours. For example, start a meet-up in your area and host it at your company.