Anybody who has been around trees for enough time is familiar with wet spots that appear on them from time to time even in the absence of obvious injury.
This happens because ordinary bacterial species found in water and soil occasionally breach a branch or trunk and enter into the plant. When these breaches extend all the way to the heartwood, the invading bacteria rapidly deplete available oxygen. Without oxygen, anaerobic processes produce gases like methane which can increase internal pressures 6-12 fold. Eventually this pressure forces xylem fluid out to the surface and the plant begins to “weep”. Arborculturalists call this phenomenon bacterial wetwood or slime flux. While this is the kind of exudate most people see on their trees, it is not particularly attractive to insects, certainly not to the degree that it would draw the attention of most onlookers.
Occasionally, though, the infection is more superficial and develops in the sapwood under the bark. Unlike the case with heartwood infections, this process ferments more of the plant’s sugars and results in a frothy cream-colored exudate that has a sweet yeasty smell. Arborculturalists refer to this kind of exudate as white or — because of one of the products of this fermentation — alcohol/alcoholic flux. Unlike slime flux, a great variety of insects find this exudate absolutely irresistible.
At this point you might be wondering whether one of the insects is playing a role in all of this. If you’ve looked at some of the citations you’ll see some of the same insects at other alcoholic flux events elsewhere. Could one or more of these be the ones that are introducing the microbes into the plant? The photographs above suggest to me that Euphoria beetles may shave away bark to enhance the flow of alcoholic flux, but that doesn’t necessarily mean they cause it. Another possible candidate might be the large orange and black cerambycid beetle Trachyderes mandibularis. A University of Florida pdf suggests – without supporting evidence – that foamy or frothy sap may arise from the oviposition sites of another cerambycid beetle, the Asian Longhorn Beetle (Anoplophora glabripennis). Unlike A. glabripennis, however, T. mandibularis only oviposit in dead wood. 
So could it be that my daughter and I stumbled on a bunch of insects seeking — pardon the pun — a buzz? And were the potential predators and their prey just too plastered to recognize each other for what they really were?