I discovered the art of brevity the day I became a mom of 6 kids.
Say it quickly, but not too fast like speed talking, boldly, clearly, with as few words as possible. Try to smile. Never shout.
Wait patiently for your words to be digested.
Wait even longer for it to click in their minds and your words to be heeded.
Proceed to the next task; for which you now have little time.
Works well for kids and writing.