Up until about 40 years ago, grandparents had no specific legal rights to interactions with their grandchildren. Those rights belonged solely to the children's parents or legal guardians.
That all changed as more and more grandparents' organizations sought help through their state legislatures and the legal system to spend time with their grandchildren. Those actions culminated with many states enacting laws allowing grandparent visitation rights with their grandchildren. Some states went so far as to allow other third parties visitation rights as well.
Then, in 2000, the United States Supreme Court made its landmark Troxel vs. Grandville decision. Although the decision did not specifically overturn all grandparent visitation laws, it did hold that a parent has the right to make decisions regarding the custody, care, and control of his/her children.
In California, like most other states, a judge may grant parents visitation rights if it is in the best interests of the child.
Some factors in determining the best interests of the child include:
Whether a parent of the child is deceased;
Whether the child's parents are separated/divorced/never married;
Whether the whereabouts of the children's parents are unknown;
Whether the child is not living with either parent.
Whether the grandparents have a pre-existing relationship with the grandchildren;
And/or whether both parents do not want the grandparents to have interactions with the children.
The fact that the children have been adopted does not automatically cut off a grandparent's right to visitation.
Grandparents' rights issues are usually very complicated and emotional for all parties involved. Therefore, it is in everyone's best interests to seek professional help from a family law specialist in dealing with these issues.