  In this work we study the footprint of a secluded dark sector with a
U$\left(1\right)$ gauge symmetry on the formation of cosmic structure at small
scales. A single generation of dark fermions with mass in the TeV range is able
to elegantly solve all small-scale issues of structure formation, while still
being consistent with the cosmological history of the universe. A new
interaction at the MeV scale is introduced for this purpose. As a
generalization we consider multiple generations of fermions as well and show
that such extensions are also cosmologically viable and allow a more flexible
choice of the parameters of the theory.
