It really doesn't make sense to try to make small children sit at attention for a couple of hours, or longer at assemblies when in fact the adults usually don't understand what is being taught either.
If you think that's bad, you should hear the JWs rationale behind it. They tell people that they don't "banish" kids to Sunday School. Now, I've been to other churches, and I don't recall ever dreading Sunday School like someplace to which I was being banished.