  The large charge symmetry breaking (CSB) implied by the $\Lambda$ binding
energy difference $\Delta B^{4}_{\Lambda}(0^+_{\rm g.s.})\equiv
B_{\Lambda}(_{\Lambda}^4$He)$-$$B_{\Lambda}(_{\Lambda}^4$H) = 0.35$\pm$0.06 MeV
of the $A=4$ mirror hypernuclei ground states, determined from emulsion
studies, has defied theoretical attempts to reproduce it in terms of CSB in
hyperon masses and in hyperon-nucleon interactions, including one pion exchange
arising from $\Lambda-\Sigma^0$ mixing. Using a schematic strong-interaction
$\Lambda N\leftrightarrow\Sigma N$ coupling model developed by Akaishi and
collaborators for $s$-shell $\Lambda$ hypernuclei, we revisit the evaluation of
CSB in the $A=4$ $\Lambda$ hypernuclei and extend it to $p$-shell mirror
$\Lambda$ hypernuclei. The model yields values of $\Delta B^{4}_{\Lambda}
(0^+_{\rm g.s.})\sim 0.25$ MeV. Smaller size and mostly negative $p$-shell
binding energy differences are calculated for the $A=7-10$ mirror hypernuclei,
in rough agreement with the few available data. CSB is found to reduce by
almost 30 keV the 110 keV $_{~\Lambda}^{10}$B g.s. doublet splitting
anticipated from the hyperon-nucleon strong-interaction spin dependence,
thereby explaining the persistent experimental failure to observe the $2^-_{\rm
exc}\to 1^-_{\rm g.s.}$ $\gamma$-ray transition.
