I am sorry that you can't see your grandkids. I know how you feel. I live in Oregon and my daughter and son-in-law live in Minneapolis. My granddaughter was born in Nov 2009 and I have seen her twice.
The only way we see her grow up is Skype. It is a free internet video chat website. It is wonderful. But her grandparents are just the "people in the box".
Luckily we will see them at Christmas.
Please discuss this situation with your Son. Tell him how you feel. They live so close you should be able to see your granddaughter more often.