We have a 7 hour stop over in Beijing. We have 5 adults and 2 children under 5 travelling.

Since you just have 7 hours, it is suggested to you to stay in the airport. You can find all kinds of clothes, books and other articles in the terminal.
The average temperature is around 15C.

Thanks Amy but we don't want to stay in the airport we want to shop in Beijing and see the highlights of the city

But will take your advice onboard......

Hello, Lisa. I think I know what you are thinking about. If I were you, I want to go into downtown, too. But I think the time is not enough for you to make a trip into city center, so I am afraid that you have to stay in the airport.

How long does it take to get to the city? I understand what you are saying but if we can just shop for a short time in the city it will be good. If it takes to long we will take your advice and stay at the airport.

The airport shuttle bus is around an hour to an hour and a half to reach the city center, so time might be not enough.

The Airport Express train is an option. According to this site, it carries passengers to the airport in twenty minutes from the city center (and vice versa) covering a distance of 28 kilometers. I myself with 3 others have a 5 hour 40 min. stop over there in April and I'm tempted to leave the airport with a stop over stamp. Or maybe a private taxi for hire in advance.