Did your daughter ask YOU to look after your grandson or both of you? If just you, it could be that your husband could feels pushed out? Do you include him in your activities with your grandson, or suggest he takes the lead on some of it? He might just be nervous about how to handle a small child again, after such a long time, or he may feels that he has had your sole involvement now your kids are grown up and resents it a little (which is understandable to a degree). Can you have a very casual conversation, to try and get his view on this arrangement and how he feels it affects him? Men are very different than women (as we know), and just an understanding of his feelings/thoughts may make it easier for you all. Best of luck!
Another Tired Kicking For The Sick And Disabled By Rishi