  Systematic measurement of $t$ and $^3$He knockout processes is planned. The
weakly-bound nature of these nuclei may affect the interpretation of
forthcoming knockout reaction data. Purpose: We aim at clarifying breakup
properties of $t$ and $^3$He by investigating their elastic and breakup cross
sections. We employ the four-body continuum-discretized coupled-channels method
with the eikonal approximation to describe the $t$ and $^3$He reactions. The
breakup cross section of $t$ is found to be almost the same as that of $^3$He
and is about one-third of that of $d$. Coulomb breakup plays negligible role in
the breakup of $t$ and $^3$He, in contrast to in the deuteron breakup reaction.
It is found that $t$ and $^3$He tend to breakup into three nucleons rather than
$d$ and a nucleon. It is shown that the breakup cross sections of $t$ and
$^3$He are not as large as those of d but non-negligible. Because about 80% of
them corresponds to the three-nucleon breakup process, a four-body breakup
reaction model is necessary to quantitatively describe the breakup of $t$ and
$^3$He.
