We Need to Talk About Kevin (2011)
The "evil child" theme has certainly been done before, but I've got to say, this film was remarkably engaging and impactful. Definitely more drama than horror, although not far off due to its horrific centerpiece event, constant psychological torment, and overall feel-bad storyline. Stellar performance by Tilda Swinton, and also by the kid who played the son during his teenage years. Highly recommended.
10/10, and for me that's rare.