Parents, the Domestic Shrine and the Life of the Soul

In general, children taught by their own parents do not suffer so much from these misrepresentations of God, as those who have been left with servants and ignorant teachers, themselves warped by a wrong early training. Fathers and mothers must have within themselves too much intuition of the Fatherhood of God not to give another tone to their teaching, and probably it is from fathers and mothers, as they are in themselves symbols of God's almighty power and unmeasured love, that the first ideas of Him can best reach the minds of little children.
But it is rare that circumstances admit the continuance of this best instruction. For one reason or another children pass on to other teachers and, except for what can be given directly by the clergy, must depend on them for further religious instruction.   From The Education of Catholic GIrls, by Sr Janet Erskine Stuart

Interesting to compare with Charlotte Mason in Home Education

Again, what child has not heard from his nurse this, delivered with much energy, 'God does not love you, you naughty boy! He will send you to the bad place!' And these two thoughts of God, as an exactor and a punisher, make up, often enough, all the idea the poor child gets of his Father in heaven. What fruit can come of this but aversion, the turning away of the child from the face of his Father? What if, instead, were given to him the thought well expressed in the words, "The all-forgiving gentleness of God"? 

These are but two of many deterrent thoughts of God commonly presented to the tender soul; and the mother, who realises that the heart of her child may be irrevocabley turned against God by the ideas of Him imbibed in the nursery, will feel the necessity for grave and careful thought, and definite resolve, as to what teaching her child shall receive on this momentous subject. She will most likely forbid any mention of the Divine Name to the children, except by their parents, explaining at the same time that she does so because she cares so much that her children should get none but right thoughts on this great matter. It is better that children should receive a few vital ideas that their souls may grow than a great deal of indefinite teaching.

Janet Erskine Stuart goes on to say:

 We speak as we believe, there is an accent of sincerity that carries conviction if we speak of God as we believe, and if we believe truly, we shall speak of Him largely, trustfully, and happily, whether in the dogmas of our faith, or as we find His traces and glorious attributes in the world around us, as we consider the lilies of the field and the birds of the air, or as we track with reverent and unprecipitate following the line of His providential government in the history of the world.
The need of right thoughts of God is also deeply felt on the side of our relations to Him, and that especially in our democratic times when sovereignty is losing its meaning. There are free and easy ideas of God, as if man might criticize and question and call Him to account, and have his say on the doings of the Creator. It is not explanation or apology that answer these, but a right thought of God makes them impossible, and this right thought can only be given if we have it ourselves. The Fatherhood of God and the Sovereignty of God are foundations of belief which complete one another, and bear up all the superstructure of a child's understanding of Christian life.
To be well grounded in the elements of faith, and to have been so taught that the practice of religion has become the atmosphere of a happy life, to have the habit of sanctifying daily duties, joys, and trials by the thought of God, and a firm resolve that nothing shall be allowed to draw the soul away from Him, such is, broadly speaking, the aim we may set before ourselves for the end of the years of childhood, after which must follow the more difficult years of the training of youth. 

 And here is more from Charlotte Mason

How to select these few quickening thoughts of the infinite God? The selection is not so difficult to make as would appear at first sight. In the first place, we must teach that which we know, know by the life of the soul, not with any mere knowledge of the mind. Now, of the vast mass of the doctrines and the precepts of religion, we shall find that there are only a few vital truths that we have so taken into our being that we live upon them––this person, these; that person, those; some of us, not more than a single one. One or more, these are the truths we must teach the children, because these will come straight out of our hearts with the enthusiasm of conviction which rarely fails to carry its own idea into the spiritual life of another. ... Let the parent who only knows one thing from above teach his child that one; more will come to him by the time the child is ready for more.

I guess with these hints (both authors give a few more specifics within the chapters I have linked to), it is easy to see why parents have such a key role.

Charlotte Mason said:

I once peeped in at an open cottage door in a moorland village, and saw a little child in its nightgown kneeling in its mother's lap and saying its evening prayer. The spot has ever since remained to me a sort of shrine. Charlotte Mason, First Approaches to God