。
Those who are children should by all means obey their parents' commands.
Literal
Child [being-たる] person all-[すべからく] parent [attributive-の] command [to-に] follow-[classical-should-べし].
Classical/archaic Japanese, preserving several classical forms. たる is a classical copula attributive ('being X') — modern ~である. すべからく is a classical adverb meaning 'one ought to, by all means' (often misused today to mean 'all, everything'). 命 read めい means 'command, order.' べし is the classical sentence-final modal 'should, ought to.' The whole sentence reads like Chinese-influenced classical Japanese (漢文調).