Lots of pictures of Halloween at the WH here:
https://wtop.com/media-galleries/2017/10/photos/slide/12/
Here’s the video of the President and First Lady greeting trick or treaters att the WH—action starts at 36:15 and continues to 1:03:20:
https://www.youtube.com/watch?v=4dgTZ5GKoiI&feature=youtu.be