What rights do grandparents have regarding contact to their grandchildren?

Grandparent rights have been gaining in recent years. But parents still hold the upper hand. The laws differ depending on location so you are best checking with the family court where the grandkids live.

Why do you ask?

What rights do grandparents have regarding contact to their grandchildren?
In Texas the grandparents have a legal right, if they are denied visitation they can go to court and have court ordered visitation rights. I hear that most judges (In Texas) do grant visitation rights to g-parents because it is in the best interest of the child to have relationships within their own family. You might want to contact an lawyer in your state.

In most states, not very much. Check with an attorney about the particulars regarding your specific state.