记住一条语法规则：若含有条件句或时间状语从句,则主句用将来时,从句用一般现在时.
He will take care of my child when I am away.
同理,本题中,He told将原来的“He will take care of my child when I am away”中的时态向前推进,变成过去时,即,would 和was.