  We present a thorough discussion of light dark matter produced via freeze-in
in two-body decays A -> B DM. If A and B are quasi-degenerate, the dark matter
particle has a cold spectrum even for keV masses. We show this explicitly by
calculating the transfer function that encodes the impact on structure
formation. As examples for this setup we study extended seesaw mechanisms with
a spontaneously broken global U(1) symmetry, such as the inverse seesaw. The
keV-scale pseudo-Goldstone dark matter particle is then naturally produced cold
by the decays of the quasi-degenerate right-handed neutrinos.
