Blue eyes turning green is a sign of acidity in the system. Your grandkids would be best to be put on a more alkaline diet, consisting of lots of raw fruits and vegetables. Meat, dairy, grains and processed sugars are all acidic.
Same thing happened to me! I was born with blue eyes, but by the time I was in grade 8 they'd turned yellowish green from my acidic junkfood, processed diet. Now that I've been doing an alkaline diet for 2 years, my eyes are slowly turning blue again. My friend who I hadn't seen in a while couldn't believe the difference in the colour.