British family relocating to Beijing

Expect quite a bit of cultural differences, mainly negative depending on your point of view.  My viewpoint is as an American who lived there 1 year and had a baby there and is mostly negative, though others who have lived there longer have a pro-china outlook. 
China is a country of kids and babies.  Everywhere you look there shall be babies in view, when outside.  Quite a bit different from the US. 
Child rearing is not the same.  Chinese hate for their children to cry and with a pro-boy, limited family system, they can easily spoil the children.  Yet in many ways the kids are better behaved than US kids.  Just bad in different areas. 
Schooling is terrible.  It is all learned by rote.  95 kids in my nieces first grade class.  The other niece has Dyslexia and China has no systems in place or even awareness of handling that issue.  Chinese are very dedicated to education but the education is designed to pass their main test at the end of high school and is not geared toward creativity or diversity.  Afterschool training abounds.  Beijing shall have some international style schools but the costs may be prohibitive. 
Pollution is as bad as you hear and shall impact your families life span.  Bronchitis, tuberculosis and other issues are much more prevalent in China. 
Food safety is horrendous.  Food poisoning is common. 
Recently they had bad vaccines they were giving to the babies.  My kid had to get reinnoculated in the US. 
Empathy is missing from Chinese society.  Those who see an issue do nothing usually to interfere or help out. 
Gambling is rampant and can destroy lives. 
Children poop and pee on the sidewalk and in public.  You shall learn the size and shape of baby pee puddles. 
There are many other good aspects of Chinese society though.  The people are generally friendly.  If you are white you might get a bit of reverse discrimination. 
TaoBao is awesome and lets you buy quite a bit of imports for some things that you may not find locally there. 
Shipping is cheap and advanced. 
In person customer service is terrible, but online customer service is excellent if you know Chinese. 
To prepare yourself watch a bunch of YouTube videos, I would say.  SerpentZa is one of the popular YouTubers. 
Contract issues with teaching can also be problematic, so you might want to prepare for that. 

Good Luck

Wow very informative.  I'm about to move there.  I hear that the best app to use there is WeChat as other apps are likely not to work? Is this true?