Have you met Principal Bozarth yet? He was also on hand and was visibly greeting everybody as they arrived.

I asked ALLIE to get a cup of water from beside the sink. When she brought it to me, I wasn't satisfied with the cup it was in. I poured it into a more acceptable cup and proceeded to pour it over ALLIE's head.
Nothing came out. She could trust me.
What they couldn't see was a little bit of powder in the bottom of the second cup. The powder? A super absorbent polymer similar to the contents of a disposable diaper. The powder absorbed the water instantly and stuck inside the cup as a "blob" of squishiness (though that's probably not the scientific term).
Now, with the trust conversation in the past, I proceeded to explain that our class is a family - that we are much like the polymer. We look after each other, help each other, and build each other up. We stick together.
Now for a changing variable - a scientific experiment: I split the goo in half and placed each half in its own zipper bag. I was careful to change only one variable in a single zipper bag: I poured a very small amount of table salt into one of the bags and left the other bag as our control. Almost instantly, the salted bag returned to liquid, while the other bag remained a squishy blob.
If our class (our family) sticks together, then it takes a single infraction (or invasion from outside forces) to split us up. We must not allow something like that to happen. We really need to work at this new and wonderful relationship.

I passed out some plastic cord and two beads to each student, and these became bracelets. The plain white beads represented their potential, their futures. It represented what they could be, what they, with effort, could become. I told them they have tremendous potential to become something beautiful - a person people could respect, an amazing friend, a successful professional, etc.
And I left it at that.
It was time for recess, so we lined up and walked outside.
When I picked up my class after their 15-minute break, my students were astounded. Their beads had changed colors! They had become something different, something "beautiful".
"Of course," I told them. "I told you that you have potential!"
During day two, I think we might hit on some essential expectations, rules, and procedures.