It sends out a very clear message: "Mess with us and we'll do something worse than kill you. We'll kill your children.

Look how we take your children and sacrifice them and there’s nothing you can do. If you lift a finger, we will destroy every last one of you. Just as we did in District Thirteen.

Don't make a threat and then not do it.

He poked his finger into my chest again. “Well, I have something to tell you: don’t let the sun set on you in this county, because…”
I grabbed his wrist and yanked him forward, tripping him with my foot. He went down back first and I caught him by his throat, three feet above the ground, lifted him up a bit and bent down to his face. My eyes glowed with murderous red. My voice turned rough with an animal growl. “Listen well, because I won’t be repeating myself, you racist prick. If you make any trouble for me or my people, I’ll hunt you down like the pig you are and carve a second mouth across your gut. They’ll find you hanging by your own intestines. The next time you hear something laugh and howl in the night, hug your family, because you won’t see the sunrise.”
I opened my fingers. He crashed on the ground, his face white as a sheet. He scrambled backward, rolled to his feet, and took off.
The three shapeshifters stared at me, openmouthed.
“That’s how you intimidate people. No witnesses and not a mark on him. Get your asses to the car.

Intimidation doesn't last very long.

Because, sometimes, things happen to people and they're not equipped to deal with them.