grandparents to unmarried couples children

I'm not quite sure what you are saying here? If my children pass way then if they are not married (as my son) then anything he owns goes to the government? Is that what you are saying? The child, due to parents not being married, would not be entitled to my son's estate?
I'm not sure that's right.

Being married provides no guarantee that your contact with a grandchild will be maintained if your ac child sadly dies?

Your grandchildren’s parents being married doesn’t guarantee that you’ll see your grandchildren as you did before in the event of the parents’ deaths. I’m not married to my child’s father and, also, I’m not young! But upon her birth we made a will which specifies who should look after our child should we both die. It is also my intention to have some instructions as to her upbringing - which I appreciate won’t be legally binding, but my child is old enough to know now what my wishes would be and arsey enough to use the instructions if required!!

I think maybe what the OP meant is a guardianship clause in a will, this can state parental wishes for education, residence, medical etc as well as assumption of parental duties.

Married or single parents should make a will and designate who will look after their children if both were to die . Oh course your money does not go to the government just because you are not married. It only goes to the government if there are no relatives at all .

My children have each designated a sibling to care for their child/ren in the case of their own premature death and this is stipulated in their wills.

there is also the matter of inheritance tax.
if they are not married, it usually means the house must be sold to pay the tax, thus causing greater stress and upheaval to the survivors.

Not only with death of a parent, but often with splitting of parents, grandparents can be cut off from grandchildren.

Grandparents can apply for a court order to gain access for visitation. Most of the time things can be settled with family mediation, but if there is resistance, then it can go to family court who will act in the best interest in the children.

It is wise to speak with your grown children to see if any mention is made in their wills.

When my children were small, my DH's brother and wife were named as guardians, but I had a clause mentioning a yearly visit to my family with the cost of travel coming from the estate.

The parents of my grandchildren have named me as guardian in their will.