  SuperWIMPs are extremely weakly interacting massive particles that inherit
their relic abundance from late decays of frozen-out parent particles. Within
supersymmetric models, gravitinos and axinos represent two of the most
well-motivated superWIMPs. In this paper we revisit constraints on these
scenarios from a variety of cosmological observations that probe their
production mechanisms as well as the superWIMP kinematic properties in the
early Universe. We consider in particular observables of Big Bang
Nucleosynthesis and the Cosmic Microwave Background (spectral distortion and
anisotropies), which limit the fractional energy injection from the late
decays, as well as warm and mixed dark matter constraints derived from the
Lyman-$\alpha$ forest and other small-scale structure observables. We discuss
complementary constraints from collider experiments, and argue that
cosmological considerations rule out a significant part of the gravitino and
the axino superWIMP parameter space.
