I'm thinking of pushing a kid into the deep end of the pool before they put their life jacket on.
Why would you push a child into the deep end?
I want them to understand they shouldn't be near the deep end of the pool without the life jacket on.
As effective as that would be at teaching a lesson, it is recklessly dangerous to treat a child that way. Given the circumstances, this child likely does not know how to swim, and you could deliberately be causing him or her to drown. This is not only unethical, but it is also illegal.
You're overreacting. Shut up.
I hope that I am overreacting, and that you were not seriously planning on doing such a thing. But I have to reiterate that if you do something like this, you could be arrested and charged with a serious crime, and you won't be able to get out of it by telling the judge to shut up.