Hi there my name is***** am a solicitor and I will answer your question today.
I am sorry to hear hat you have had this horrible experience and that you are still affected by it.
I should think that, yes, your school was negligent in failing to contact your parents promptly, and directly, when the incident happened.
However, their best defence may be the passage of time in the meantime. One has to take a personal injury action within two years of the injury. As you were a child when it happened, the defence would argue that the clock would have started running when you were 18, so you would have been out of time when you turned 20. Alternatively, the clock might start from the time when you became aware of the effect on you of the incident in question. So, the question may be, when did you first become aware of the issue and/or disclose it to anyone?
Certainly you will have to deal with that issue. However in cases like this people are often unable to disclose or realise the impact that the experience has had on them for many years, so that litigation can sometimes go ahead many years after an injury has occurred.
I would strongly advise you to consult with a Solicitor directly about this right away, so that you can take immediate action if appropriate. Just pick up the phone to any solicitor in your area and ask to make an appointment to discuss a personal injury.