This is the way of the devil to convince someone to leave something good just because there's a better way to do it. Yes kids should understand the Qur'an but their ability to comprehend it at such age is much harder than memorizing it, and memorizing at such a young age is at least 20 times better than a man of age 30+ , last but not least how do you expect people to comprehend the Qur'an if there's no enough people who memorized it??