What type of visa? Help !! Thanks

We are UK citizens - 2 adults and an 11 year old. We are going to Abu Dhabi in March 2019 from Manchester UK and from there flying to Beijing for 5 nights and then back to Abu Dhabi and then flying back to the UK.
What type of entry permit do we need and what is the cheapest way of doing this please?
Also how and where do we apply for them?