This is a question we get almost weekly at our law firm during initial conferences. Often, after reviewing the case with our client, it is our opinion that the grandchild or children would be better off with the grandparent or grandparents in that particular case. However, we advise the grandparents to "tread lightly" if there is nothing seriously wrong with the mother or father, because they are tough cases to win. The grandparents are in the "second tier" of preferred custodians of the children and are not treated with equal footing by the courts. In other words, it is an uphill battle always if there is not significant proof that the children are seriously neglected by the natural parents.
You can review my Blog Post on the subject here at that portion of my website for more details.