Liturgy, it is said, is the life of the Church. The word itself means "work of the people." It originates in pagan Greek practice, where the wealthiest Greek citizens of a city-state would ritually donate warships, plays, public buildings and festivals to honor the city of their birth and give delight to its citizens.
Christians began using, in their own buildings, the adaptations of Jewish Temple ritual that Jesus had taught them. Christians called their ritual "liturgy" to show that it honored the City of God. The rituals that Jesus empowered with the grace of the Crucifixion were performed by Christians in order to deliver the sacraments and the divinizing grace of those sacraments to the people. This makes the people holy and thereby builds up the City of God. Just as with the pagan Greeks, the divine liturgy" was the "work of the people", but unlike the pagan Greeks, Christian liturgy actually carried divine power. In part, the divine liturgy makes up what is lacking in Christ's suffering, for the sake of the Church, just as Colossians 1:24 promised to do. By using the pagan Greek word to describe God's work in their lives, the Christians helped pagans understand the Paschal Mystery and the Body of Christ.
Jesus was both human and divine, so the liturgy is work done by human beings, but carrying divine power. The Mass is about the Passion, Death, Resurrection and Ascension, which are the four aspects of the Paschal Mystery. Each of the four aspects of the single act which is the Paschal Mystery is itself inexorably linked to one of the four reasons for Christ's Incarnation (CCC 457-460). God became man to To show us how much He loves us (Passion), To save us from our sins (Death), To give us a model of holiness (Resurrection), To divinize us (Ascension).
Thus, the Mass is always about those four actions and those four reasons.
So, what does a screaming toddler have to do with any of this?
Does the toddler make you suffer?
Ohhh.... poor you.
Does the toddler force you to die to your self-perceived facade of holiness because you suddenly find less than serene thoughts floating through your mind?
Oh... that must be terrible for you.
Does the toddler give you the opportunity to rise above your petty selfishness?
Does the toddler give you the opportunity to again climb the mountain back into the liturgy, this time with a better understanding of your own failings in charity towards others?
Why, this is most excellent!
Were there screaming children watching the condemned men process up the road to Calvary? I bet there were. Did Golgotha have a cry room? Call me a skeptic, but I doubt it.
The Mass is the life of the Church, and my life is my life before God. In both of these lives, there are screaming children, children acting out, children running up and down aisles, playing with toys instead of paying attention, children even trying (succeeding?) in running into the sanctuary during Mass. The difference between children in the life of the Church and the child in MY life, is that the child in MY life is ME.
I scream when God offers me holiness, I ignore His call, I play with toys rather than pay attention, I run up and down my every day life without thought nor care of God. That child acting out in front of me is a visual representation of ME, every day, even AFTER I have had my morning coffee. That's why so many of us hate hearing children at Mass. Those kids are way, way too much like offensive little ole' me. If I don't want my own self-perception pierced, then I damned well can't have children around showing me off to myself.
Get thee to a nunnery!
Or a cry room.
Or anywhere, really, but in front of me. This glass is not darkly enough, I can still see into it. I don't want face-to-face, I want the picture of Dorian Gray in front of me, so I can pretend it is my mirror. Let me have children about me that are fat, Sleek-headed children and such as sleep a-Mass. Yon screaming child has a lean and hungry look. He suffers too much. Such children are dangerous.
This child is ... this child is... this child is a living, breathing, sobbing tableaux of the Crucifixion, and I am really not able to face Christ crucified. Give me the quiet Mass and its quiet illusion of quiet. Take away from me this image of the bloody, snot-streaming Christ. It offends my gentle holiness.
Yes, it does.
And that's a GOOD thing.