Consider your choice of light and time of day . If photographing in the day try turning the children so the window light falls onto their faces. But in day light you may not be able to capture those gorgeous tree lights. If you want glowing lights from the tree, you will want to shoot when it is dusk or dark. The challenge here is then how dark it can be and how high you need to push your ISO. Tip: why not add additional lights on your subject, for example: an iPad, torch on your phone or fairy lights.
Aim for a low aperture to create those gorgeous blurry lights on the tree. (ie bokeh) eg F2.8 or lower if you can! This will depend on your lens choice.
Settings – have a go at the following as a starting point and tweak according to light and how they look in camera. If you are shooting in the daytime try an ISO of 800-1600, aperture of f1.4 – f2 (or the lowest F Stop you can) and set your white balance a little warmer to around 6000 Kelvin (or cloudy if your camera cannot be set in Kelvin). If you are shooting into dusk, or when it’s very dark, you need to push your ISO much higher and balance your shutter speed accordingly. Eg 1/200 second shutter speed, 1.4 aperture and 6000-8000 ISO! (Which is a little high but necessary if your light is so low)
Get creative … try putting fairy lights in front of your subject rather than behind!
Look for reflections! Eg maybe in your floor, windows and door.
Macro photos. Photograph some close ups of all your beautiful decorations.
Most professional photographers will lean towards shooting when its dark to take full advantage of the Christmas tree lights and to make the images feel like they are straight from a Christmas card. It is certainly more challenging to shoot at this time but have a go!!
If you are struggling to focus your images in low light use a phone light to shine towards your subject.
Create natural expression from your children! Use a family member to make them smile. Get them to stand behind you and your camera so they are looking towards you. Try bubbles or a feather duster with toddlers!
Have fun! Don’t get hung up on posing your children but enjoy the moment!