First of all there are practicalities involved.
You need your window fixed ASAP in this weather so that ball has to start rolling (and apparently it has). Also these are your neighbors so obviously you want to maintain civility at all times for the sake of the long term.
Also I'm guessing it's an expensive window so you're not gonna get financial compensation from the neighbors.
This means that it's an insurance job.
However there's still the matter of the Mom and kids (no Dad?) next door. You DON'T circumvent the Mom. She is their legal guardian and they are the legal wards. You have to approach her. Do so with the drinking glass. Explain to her the story. The noise of the kids playing outside, the silence, the discovery of the broken window, you knocking at the door and being totally ignored by the kids, the discovery of the glass.
It kinda sounds like an incident of underage drinking while Mom was gone. Let her know the situation and ask her if she can talk to the kids about it. Let her know you're concerned that your insurance premium is gonna go up (I don't know whether this is true). Tell her that anyways. Don't be accusatory. Some parents get VERY DEFENSIVE to the point of being offensive and stick up for their kids even when the kids are wrong. It's a common error in parenting I see quite often. If you sense a conflict is arising, abort mission.
The best you might hope for is a confession and an apology. If you're lucky you might even get a "sorry gift."
But you did your part by keeping Mom in the loop and keeping the kids accountable. They know what to expect from you as you've laid down a clear (if forgiving) boundary.
That's about all you can do.