GameManager.cs

void ClearField()
    {
        GameObject[] targets = GameObject.FindGameObjectsWithTag("Target");
        foreach (GameObject target in targets)
        {
            target.GetComponent<TargetExit>().Exit();
        }
    }

TargetExit.cs

public void Exit()
    {
        if (this.GetComponent<Animator>() == null)
            // no Animator so just destroy right away
            KillTarget();
        else if (!startDestroy)
        {
            // set startDestroy to true so this code will not run a second time
            startDestroy = true;

            // trigger the Animator to make the "Exit" transition
            this.GetComponent<Animator>().SetTrigger("Exit");

            // Call KillTarget function after exitAnimationSeconds to give time for animation to play
            Invoke("KillTarget", exitAnimationSeconds);
        }
    }