Baha’u’llah explains what the children should be taught first

That which is of paramount importance for the children, that which must precede all else, is to teach them the oneness of God and the laws of God. For lacking this, the fear of God cannot be inculcated, and lacking the fear of God an infinity of odious and abominable actions will spring up, and sentiments will be uttered that transgress all bounds... parents must exert every effort to rear their offspring to be religious, for should the children not attain this greatest of adornments, they will not obey their parents, which in a certain sense means that they will not obey God. Indeed, such children will show no consideration to anyone, and will do exactly as they please. (Baha’u’llah, The Compilation of Compilations’, vol. I, Baha’i Education)