Did you think that the Sacrament of Penance wasn’t part of this discussion on the sacramental life of children? Read for yourself:
However, in the precise determination of “the age of reason or discretion” not a few errors and deplorable abuses have crept in during the course of time. There were some who maintained that one age of discretion must be assigned to reception of the Sacrament of Penance and another to the Holy Eucharist. They held that for Confession the age of discretion is reached when one can distinguish right from wrong, hence can commit sin; for Holy Eucharist, however, a greater age is required in which a full knowledge of matters of faith and a better preparation of the soul can be had. As a consequence, owing to various local customs and opinions, the age determined for the reception of First Communion was placed at ten years or twelve, and in places fourteen years or even more were required; and until that age children and youth were prohibited from Eucharistic Communion.
There was not a universal practice before QS; it seems that we still have this legacy with Confirmation.
This practice of preventing the faithful from receiving on the plea of safeguarding the august Sacrament has been the cause of many evils. It happened that children in their innocence were forced away from the embrace of Christ and deprived of the food of their interior life; and from this it also happened that in their youth, destitute of this strong help, surrounded by so many temptations, they lost their innocence and fell into vicious habits even before tasting of the Sacred Mysteries. And even if a thorough instruction and a careful Sacramental Confession should precede Holy Communion, which does not everywhere occur, still the loss of first innocence is always to be deplored and might have been avoided by reception of the Eucharist in more tender years.
Not such an innocent age, this 1910. Remember that the experience of slavery was not unknown a century ago. And an even wider population of children were pawns in games of economic exploitation and profiteering in the industrial world. Saints might be expected to transcend such evils. Clearly Pope Pius X was of the mind that sacramental graces were vital to the spiritual health of individuals and of the Church. QS 7-8 has strong language: deplorable abuses and even evil resulted from the denial of the sacraments. No less true today, I would say.