I'm not going to bring my nephew with me to his grandparent's house.
Why don't you bring him with you?
He's annoying, I don't want to deal with him while I'm there.
If you agreed to take him to his grandparent's house you should do it.
I did tell him I would, but I changed my mind.
If you told him you would take him as a favor you should do it. He will feel disappointed if you don't do what you promised.