Is it ok for 5 year old diabetic to eat sweets daily?

I am worried about my 5 year old nephew.  He is a diabetic and his blood sugar levels go from extremely high to extremely low on a daily basis.  I don't want to judge his mother and cause family problems, but she allows him to have sweets daily and the majority of his meals are loaded in carbs.  Is this ok? And what can I do to tell her in a non offensive way if it's not?

[VDKALVR]

look up what happens to the human body with extreme highs and then lows, (kidney failure,loss of vision, loss of limbs,ect) and inform her that her actions may lead to such things.  Any parent should hopefully think about their way of life and how it affects their children.  I wish you luck in trying to find a way of dealing with this.  And fyi-sweets are not good in daily or high doses, the occassional piece of birthday cake no issue, but this is what is causing his blood sugar to go high, then the sugar is used quickly and he crashes (hence the lows).  High carbs tend to leave the body with high sugar but even then he will go low unless there are other foods that help to balance the blood sugar.  It sounds like she needs some serious diabetes education before she causes severe damage to her childs health.