The letter no parent wants to write: A mother's 'thank you' note after son's tragic death.

Light for Riley is an Australian charity that aims to protect families from vaccine-preventable diseases. It was founded by Catherine and Greg Hughes after they lost their four-week-old son Riley in March 2015. Their work raises money for the Princess Margaret Hospital Foundation in Perth and generates vaccine donations for UNICEF. Here Catherine says thank you to those who supported her during her son Riley’s fight against whooping cough.

Thank you to the nurses who helped entertain our daughter with toys and games when Riley was dying in hospital.

Thank you to the clever doctor who correctly diagnosed Riley before receiving the swab results back, just by the sound of his cough.

Thank you to the PICU doctors and nurses who kept us calm in an environment where you feel sad, desperate and scared.

Thank you to the doctor who told me there was a chance Riley could die. I didn't like you at the time, purely because your words felt like huge punch in the gut, but it was important we were prepared.

Thank you to the kind nurses who tried to make sure we ate, drank, and rested when all we could think about was whether our son would make it or not.

Thank you to the doctor who put her own family's life on hold while she worked tirelessly, staying back late and coming in early.

Thank you to the doctor who sat with us in the family room with the unenviable task of telling us that it was unlikely Riley would survive.

A few days after these footage was taken, Riley lost his battle with whooping cough. Post continues after video.)

Thank you to the nurses and doctors who gave us time and space to say goodbye to our son as he passed away in our arms.

Thank you to the young nurse who came down to PICU after she heard that he didn't make it, and cried with us.

Thank you to the nurse who carefully took his little hand-prints and foot-prints for us.

Thank you to the nurse who held our son's body in her arms as we left the hospital, sobbing.

Thank you to the nurse who stopped us in the hallway as we left, shocked that he didn't make it, and hugged us tightly.

Thank you to the nurse who came to Riley's funeral and said such kind words to us.

And thank you to all the incredible doctors and nurses out there who talk to patients about the importance of vaccines, and what can happen when babies who are too young to be vaccinated contract a vaccine-preventable disease.

Doctors and nurses don't just save lives - they do so much more.

I know sometimes they receive a lot of abuse, but they really deserve our gratitude and thanks for all that they do.

x Riley's Mum

This post was originally published on the Light for Riley Facebook page and republished here with permission.