I would recommend "The Abolition of Man" by C.S. Lewis. He argues that in all (classical) religions, there is a common core of morality, and that it is foundational. All our modern "ideologies" are an over-focus on one aspect or another of that common core.

I wouldn't have your kids read The Abolition of Man, but you might find it useful in thinking about this question.

Note well: I've had to re-read it several times over the course of several years. Lewis writes very simply, but there are some very deep ideas in there.