A few of my choir members have small children. Now that we’re incorporated into the back two to three pews, families are somewhat integrated into the music area. And I’ve noticed that ubiquitous church breakfast cereal, like what is described here. Michelle Francl:
As I knelt after communion, a little face popped up in front of me, her bag of Cheerios in hand. She ate one and flashed a contented smile. Meanwhile, we are singing “I am the Bread of Life, you who come to me shall not hunger…”
It occurred to me that parents who bring Cheerios for their kids are teaching them that the Mass is a place where their hunger can be fed. And is that such a bad thing?
I think not.
On the other hand … last week I noticed an empty juice box stuffed in next to the hymnals. It’s wasn’t sticky or gross. Just left in a “convenient” place. I wasn’t bothered too much by the find, and found a place to dispose of it soon enough.
I think it is difficult to forbid parishioners on such things, and guests probably impossible. To what degree should parishes discourage or even encourage it?
Catholic Sensibility 
I don’t know whether or not the practice should be discouraged. What I do know is that my parents generation did not bring such treats. In those days everyone fasted from midnight until after receiving communion. Also very young children were rarely seen in church. In my childhood parish there was a nursery ministry where parents dropped off the little ones. My siblings and I stayed home with Grandma who was too old to go to church, or so we were told.