Before you do anything else on your devices it’s easiest to setup your XBOX live accounts first.
XBOX Live allows you to create an account for yourself and then sub accounts for your children (although they will all need a valid email address) so you can control their privacy settings etc dependant on their age and how nice you are feeling!
Create your own account
First up create your own account as a parent. This will give you global access to your kids accounts and you can also use it on any other Microsoft sites.
https://signup.live.com/ will redirect you to the appropriate page for your country.
Here you will be asked to complete basic details about yourself in order to create an Microsoft account to use with XBOX Live and then in turn Minecraft Personal Edition.
Once complete hit CREATE ACCOUNT and await your verification email from Microsoft.
When you receive the email you will need to either click on a link or type in a 4 digit code to verify you have received the email from Microsoft.