I read that Damu Anna was childless. How did Sai Baba help him with this problem?

Yes, that's correct. The Shri Sai Satcharitra mentions that Damu Anna had two wives but was without any children, which was a source of suffering for him. His situation changed through his faith in Sai Baba. As Chapter 25 explicitly states, it was by receiving Sai's blessings that his desire was fulfilled. The text confirms that he was subsequently blessed with sons. This event is presented as a powerful example of how Sai Baba wards off the misfortunes of his devotees and grants their desired objects when they have one-pointed faith and devotion.