The inspiration for this scenario came for a Romeo-and-Juliet type story in the Balkans that Mervyn and I heard about. 

» An imaginary town, designed to be adaptable to various cultural contexts. The town is in an imaginary country that descends into civil (or ethnic) war. The timeline is intentionally stylized and condensed.
Since, sadly, we are now used to such conflicts, the basic duality between a community that has been divided into two sides does not need to be explained.
» Across the front of the stage, a street. In the middle of the stage, front to back, another street (e.g. at right-angles to the first one)
» Either side of this street, blocks of houses (or other suitable buildings depending on the cultural context)

» Two children, in the age range 10-14, who live on the opposite side of the street and who are friends. They can be either sex. I have not yet named them, and will probably allow a variety of names with similar syllables/sounds so that they can have names that suit the cultural context of where the opera is being performed.
For the purposes of this scenario, I have called them Hanna and Joseph.
» Their parents, formerly friends
» Two gangs of children from opposite sides of the street. This chorus will include a number of solo line(s) to allow children smaller solo roles
» A UN officer and soldiers

The action is continuous, but for convenience I have divided it into sections

Section 1
Joseph and Hanna are playing in the middle of the street. They are worried by the way people are becoming bitter and enemies, and about the fighting that is coming closer to the town, and they don't understand why.
Joseph's parents come out of their house, see the children playing, and hurry over, pulling Joseph away. Hanna manages to whisper to Joseph to meet her later. Hanna's parents hurry out of their house. The two sets of parents abuse each other, on ethnic/religious lines, but without any reference to any specific ethnic or religious group. They make it clear that the two children are to have nothing to do with each other. Joseph's parents return to their house with Joseph. 
Hanna questions her parents - the two families were friends - what has happened, why can't she see Joseph. Her parents 'explain' the changed situation, that their friendship was wrong, and that Joseph belongs to people who do not deserve to live in the town... They enter their house.

Section 2
Off stage children's chorus, sounds of argument, crying. Joseph and Hanna sneak out of their houses to meet, but this time instead of meeting in the middle of the street and playing, they meet in the shadow of the street. They discuss what their parents have told them. They decided, anyway, that they will remain friends whatever happens.
As they do so, two gangs of children appear from opposite sides. They castigate Joseph and Hanna respectively, pull them into their gangs. They two gangs taunt each other, mirroring the parents of Joseph and Hanna in their own fashion. Two kids eventually get into a fight in front of their gangs. In this section Joseph and Hanna are still troubled by this hatred, but they are now under peer pressure to join sides.
Distant small-arms fire. The parents from each side tell the children to go home, as it is getting dangerous on the street. Two gangs exit in their opposite directions, still taunting each other.

Section 3
Joseph's mother is  left alone on her doorstep. She sings about her fears for her house and the safety of her family, but not about the underlying madness of the situation, which she does not recognize.  (This may be a double solo with Hanna's mother independently having the same fears on the opposite side of the street). Gun fire still heard.

Section 4
The gang with Joseph in it returns. They now geared up for action, aping the movements of soldiers entering a hostile town (moving along the sides of houses in single line, being hushed by the leader, etc.)
Joseph has now been convinced of the need for the hatred of the opposing side, and wishes to prove himself to his peers. The gang cross the street and breaks the windows of the houses on that side.
The opposing gang issues out, pulling a reluctant Hanna with them. The two gangs take up positions on either side of the street, but now they are more serious than their previous encounter. They use street items to set up barricades. They hurl objects across (these can easily be physically harmless on stage). 
Hanna has had enough. She asks them what they are all doing, pointing out individuals on each side who were once friends, saying they must stop this. Joseph, from the other side, now taunts her, saying his friendship was a mistake, she is as bad as the rest of them. Strong support from kids. Uproar.

Hanna is still determined to try and stop the confrontation. She steps out beyond her barricade into the street, and again appeals to both sides to stop. A child from Joseph's gang pulls out a gun, and shoots. Hanna falls, hit. There is stunned silence from the children, and then cheers from Joseph's side, congratulations to the child with the gun, and fascination with the gun itself.  Still gunfire in distance. 

However, Joseph is horrified, seeing the actual results of his hatred. He breaks through his gang, and runs to the fallen Hanna. There is a very short duet between the two, cut off by a gun shot from Hanna's gang. Joseph is hit, and falls. Cheers from the other gang. The guns are pointed at the opposing gangs. Children take cover. 

As they do so,  UN troops enter in a column along the street that runs to the back of the stage. The children fall silent. The UN officer goes to the two fallen children. Joseph is dead, but Hanna is still alive, and is tended by the UN soldiers, and taken out on a stretcher. 

 The UN officer looks at both sets of children, and takes one of the guns from the child that is holding it. He then picks up the dead Joseph, and shows him to the children. He tells them that this what war really means, that the child is the same flesh and blood as they are, and is now dead, and this is where hatred leads. The children largely respond - the horror of it is dawning on them. 

Joseph's parents rush up, venting grief but also anger and spite at the opposite side. The UN officer, still holding Joseph, says, no, it was you with your hatred that killed him, and that this can no longer continue. Joseph's father is angry, abusive; Joseph's mother is distraught, her worst deepest fears - the death of her child - have come true. 

 Some of the children from both groups join him, for they don't want it to happen again. Within this closing chorus, with its positive message, the dangers are still apparent: Joseph's parents taking his body, still angry, and the child with the other gun, who hides it for future use. The opera closes.