Jared Kushner has played an important role in Trump's campaign, helped him get elected and even wrote speeches for him. I imagine he will continue to be a close adviser to his father-in-law. He and Ivanka have already made plans to move to Washington. The two are about as liberal as you can get, and one of Ivanka's priorities is climate change. To think that Trump's children who are all entrenched in the elite business community and have positions in Trump's business dynasty wouldn't play some sort of role in his presidency is naive.
As a side note, I don't think it was so much anything Chris Christie did as a reason for Trump not placing him in his cabinet, but rather the fact that Christie sent Jared's Daddy to prison! Having Christie and Jared circling around each other obviously wouldn't work out so well. Christie isn't family so he's out.
