Never again can children be told cheaters never win.
We just saw our future stolen from us with the confirmation of an unqualified justice who was nominated and voted on by an illegitimate president and treasonous congress. 
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And ignorance doesn't matter at all.
One of the reasons children begin looking askance at their parents is because they learn early, and I do mean early, that their parents are lying to them.
Just to let you know, a 2 year old knows when an adult is lying and they fully understand what "NO" means by then. Thus begins their sneaky suspicions about the world and what they are told. You can tell them it has to do with their age and skill level, but then their see their little toddler friends in play groups and other socializing functions, and well...children aren't dumb, people. Not in the least.
How the world should be as opposed to how they see it operating.
I believe some studies have shown that children know a lie earlier than two. But the concept of the word "No" being fully instilled can and does connect the dots for them.
While I agree with teaching children the best about humanity, I am not one to lie to a child about the reality of the world they inhabit.
I do keep it age appropriate though. Still, I don't lie to children and that has caused some harsh feelings with my friends over the years. But never with their children. 
Teens and younger often think their parents are stupid or they don't understand, or it is different now, because of the lying. Children are not dumb - neither are they as fragile as you might think. Always exceptions - act accordingly.
They see the world as it is, at least the world they inhabit (school, friends, teams, etc..), and they hear from their parents how the world should be. Don't cheat. Don't steal. Don't lie. It always gets you in the end. But...they have already witnessed repeatedly that such is simply not true.
Instead of telling them not to cheat and saying cheaters never win (a falsehood), tell them the ethics behind it instead and what it takes to be a decent person. Keep it age appropriate and NEVER lecture (I know, I know). Keep it open ended and use props - books, movies, real life situations, whatever. There is a damaging side to lying and cheating, but it's not always the liar or cheater who sustains the damage - show them the victims. Empathy. Sympathy.
I've been out of the early childhood development arena for a long time now. So what do I know?
Republicans? Cheated. And won.
Patriots? Cheated. And won multiple times.
Alex Rodriguez? Cheated. And won.
Curt Schilling? Cheated. And won.
Lance Armstrong? Cheated. And won.
Cheaters never win? Cheaters always win! 
