I would wonder where they had learned how to do this and what was motivating them. I have not really met this situation before, but I would be tempted to ask the offending preschooler to meet with a teacher and the two other children to explain what they did and to apologise for their behaviour. This child also needs to listen to the feelings of the other two children, and to help them mend their relationship in some way.
Whenever children have been unkind to others, it is good to get them to do something kind for them in response—to teach positive and caring behaviour. It is important for the child who was setting the other two against each other to know that this is very hurtful for the other children, and to listen to their feelings.
I encourage and coach older children to use the following model; you can modify it to make it age-appropriate:
What to say when you are hurt by someone
“In this situation . . . when this happened . . . I felt . . . and it would help me if next time you would do . . . and then I can help you by . . . . What ideas do you have that would stop this happening again?”
Age-appropriate alternative
“When you said/did . . . , it made me feel . . . . I will feel . . . if you did . . . .”
What to say when you hurt someone
“I am sorry that I hurt you by . . . . That was wrong. Please forgive me when you are ready. Next time I would choose to do . . . instead.”
Age-appropriate alternative
“Sorry for . . . . Please forgive me. Next time I would choose to do . . . instead.”
In addition, it sounds as if the offending child may have experienced a deep hurt in their life. It would be good to find out what this was and to help them get help for their hurt. It may be that they have suffered an adverse childhood experience or some kind of broken attachment experience, where other people may have let them down.
Any advice given is general in nature and is not intended as a substitute for medical advice and must not be relied upon as such. For any healthcare advice, always consult a healthcare practitioner.
