To whom it may concern,
This young person has Type 1 Diabetes and is prescribed insulin injections. They will therefore be required to travel with needles, insulin pens and a meter to monitor their blood glucose concentration throughout the duration of the flight. It is essential that these be held in the hand luggage.
They will also need hypoglycaemia treatment in the form of sweet food or sweet drinks with them at all times.
I trust that this letter will facilitate the young person through customs.