Before you wrap your children's presents, read this.
Don't wrap your device yet!
First things first - set it up. Don't wait until Christmas day. If you have games consoles, do yourself a favour and do the updates first. Plug it in and set them it on the home wifi before Christmas day. Often consoles do a huge update when first turned on and user accounts need to be created. On Christmas day you wont have time as the beers, wine will be ready to drink and the turkey will need attention.
When you set up any devices you will want to manage content (the stuff that you don't want the kids to see), spending, screen time and also see some degree of reporting of their activity.