Gavin really really doesn't like sleeping on his own, mostly on account of the constant night terrors he suffers from. Zayne and Shiloh have by this point gotten used to having the little fuzzball sleeping between them knowing its going to a fairly long time until they had the bed to themselves again.
And while he'll deny it, up and down, left and right, to his grave, Shiloh actually does like being able to comfort his son. Using his dark magic to calm the boys chaos filled mind and replace his horrific nightmares with sweet dreams.