I would say first pray and believe that God is going to open doors for you, that He will give you favor with DHS...Then, if you can, go get a lawyer and try to get custody of this grandchild...
Father we come before You asking that You give these grandparents favor with DHS and that they really investigate this matter again, give someone a bulldog tenacity to investigate until they come up with the truth...Father help these grandparents get custody of their grandbaby until the parents are able to take care of him or her...Thank You Lord that You are opening doors for them this night in Jesus name amen !!! We give You all the Glory Lord !!!
Never give up dear ones...God knows and He sees all that is going on and He will make a way for you !!!
