  In this paper we show how the method of Lie algebra expansions may be used to
obtain, in a simple way, both the extended Bargmann Lie superalgebra and the
Chern-Simons action associated to it in three dimensions, starting from $D=3$,
$\mathcal{N}=2$ superPoincar\'e and its corresponding Chern-Simons
supergravity.
