Suggestions how to keep an older child from frightening younger one by threatening to tattle to a parent?

In an afterschool program a child 2-3 years younger became unglued when an older child in the program was being too bossy. (I can tell he has been able to do this before-I sat him out once already.)Suggestions how to keep an older child from frightening younger one by threatening to tattle to a parent?
haha kids these days have no sense of direction