1. Wait for night (this was hard for me. You can tell in the picture with both boys that I didn't wait for it to get super dark.)
2. All of the lights off except the tree. I used a lamp across the room to cheat a little and give me a little light.
3. Camera in manual mode with the following settings as a guideline:
Aperture all the way open (mine was f 1.8)
Shutter speed slowish (mine was 1/250)
ISO super high (mine was at 5000)
>>> NO FLASH! <<<
Shameless plug - I teach a basics of photography class that will teach you what all of these thing mean :)
4. Snap way! Who cares if they're technically perfect - have fun with your kiddos. The picture of Landon above... he was calling our tree a gum-nut. I'm not even sure what that means but he thought it was hilarious and made for a cute picture.
Full disclosure, I did edit my final pictures just for personal preference.
You can also do these types of pictures during the day for a different, but still fun, look.