How early can you get diabetes?

I had a patient coming from U.S. He is there since last 20 years.He came with his wife and two boys,14 and 12 year old. These children were born in America and so they are American children (of Indian origin)

While treating my patient I asked for the blood test of the boys for hemoglobin,vitamin B12 and D3. But my patient took the package for a number of tests, which included HbA 1c
and average blood sugar.

Both the boys were border line diabetics. I was shocked.
I had never asked for this test ( I never thought on those lines)   

Obviously, the diet they were having there was the cause.
Breakfast was cereals which have high sugar content.The lunch is in cafeteria at school which is fast food(only)

These boys did not carry lunch box from home. (their mother was also not insisting) They used to have snacks the whole day,like candy, biscuits, chips, rice crisps, coke and other sugary drinks.

The dinner was home cooked, which was just rice, dhal and a vegetable some times.

High GI foods are fast foods, breakfast cereals
Low GI foods are wheat, rice, chole,, rajmah, mung, mutter,curds, fruits

The blood glucose levels in these two boys are high due to the fast food. They are on the border line but the average blood sugar was still normal (less than 140)

This is due to high secretion of insulin in response to high blood glucose. But how long? Pancreas will get exhausted one day and insulin secretion will start falling.

There is chaos inside at present.

It is like driving the car in the first gear. How far it will go?  

I talked to the whole family and asked to change the dietary pattern as shown in these pictures.

P.S.

The family has gone back to U.S. 
Will they follow my advise? I do not have high hopes.

Eating is a behavior and behaviors do not change overnight. It needs a conscious efforts for a long time.

If they do not change, I am really afraid that these two boys will become diabetic in a few years.