Legal Question in Family Law in California

I assume you are asking this under California because the child(ren) live(s) in California. Under California law, grandparents have no legal right even to ask a court for any visitation, much less get any. Custody rights belong exclusively to the parents. During each parent's custodial time, however, they are perfectly entitled to let the child(ren) visit relatives anywhere in the U.S. unless there is some reason it is bad for the children and there has been a court order against it. So the parent who agrees is free to send or bring the kid(s) to visit you on their time. If they don't already have two weeks in the summer to share with you, they can also go in and ask for a custody modification so that they have the custodial time needed to let the kids visit you.