The news of David’s flight from Gibeah had reached his family. Knowing that King Saul was likely to be watching them and that they were in danger, his family went to join him at the cave. They probably expected David to be able to support them/protect them in some way.
1 David departed from there and escaped to the cave of Adullam. And when his brothers and all his father’s house heard it, they went down there to him.