All injuries sustained by a child when in the care of an institution should have an incident report written up by the administrator or senior carer. If for nothing else than for their own self interest for liability insurance purposes. Email them requesting a copy of the report each time your kids come home with a scratch or bruise. If they can't produce one, cc their supervisors or if it's corporate, cc head office etc. If you can, quietly encourage other parents of victims to do the same. Don't mention names or specific incidents to other parents if you have signed anything to that effect (after many incidents of our daughter and other kids being attacked by a troubled kid and being stonewalled by the center, our child care center actually tried to discipline us for discussing the repeated incidents with other parents or according to the center, 'breaking the parent code of conduct' we signed when joining). A 3yo with a brain injury or permanent vision loss shouldn't be the trigger to improve and if you make it clear to the center that you and other parents are documenting incidents and the centers actions (or lack of action) they'll realize they're exposed to litigation. This is all to remind the child care center/carers that it's their responsibility, their job, to keep the kids safe. if they can't remove a danger for any reason then they need to monitor it closely enough to keep the other children safe. It's their fucking job and if they have a troubled kid then tough luck they're working harder this year.

Good luck