Unlike man to man defense, you don't even have to apply good defensive principles to be effective at the youth level.
First, we commend all youth coaches for taking up such an important role in developing children! In the grand scheme of things, what defense or offense you pick doesn't matter in regards to how we develop the children's character on the teams that we coach. Second, I think we can all agree that we want to develop better basketball players for the future and we want what is best for them.
Now, one of the most-debated topics is what defense should we teach youth players? Zone, Match Up, Pressing, Man, Amoeba? The answer is without a doubt man-to-man defense! I can promise you that in the long-run, you will develop better basketball players by playing man to man defense.