I'll debate that one with you - we have always taken our kids, since they were little, to after hours events. You just have to manage accordingly, i.e. not expect them to go from park open to midnight, etc, or to get up for 6am open the next day. (however, we have done that...lol).
Our MK portion of our trips is frequently ONLY a party or after hours event. 4pm-midnight or 1am is a pretty good deal for the price, without the heat, and hopefully smaller crowds (not lately, though). We have done this since 2012, when our kids were 4, 2, and 0.