1 day in January in Beijing with Kids - Suggestions?
 

We will be passing through Beijing on our way back to the States from Thailand in early January. We will have a 9 hour layover and are planning on leaving the airport for the day (yes, we know about the TWoV - its on another post). We would like to see some cool sites that day, but not sure what makes the most sense.
We have 3 kids (ages 11, 11, and 8), and will be coming from Thailand, so we won't exactly have brought a ton of layers with us. I wanted to go to the Great Wall at Mutianyu, but I hear it might be just too cold for that.
Any suggestions to give the kids a quick taste of China, but without needing to pack a whole suitcase of extra luggage? Or assuming we do bring some warm jackets, would would people suggest at that age? Could they still do the toboggan ride at Mutianyu if there is snow on the ground?

It is unlikely that you will have snow although not impossible. Beijing is very dry in winter and you can go a while month with no precipitation.
Mutianyu is still an option in winter as it is easy to get to from the airport. you should arrange for a driver ahead of time for this.
It would be useful to know at what time you land and depart as this would influence my suggestions.

We arrive from BKK around 6:30am, and our flight to SFO leaves PEK at 4:00pm. We are considering just bringing a suitcase of winter stuff and leaving it in Bangkok for the week we are in other parts of the country, just so we will have it in PEK.

Going to the Great Wall is wonderful for kids. Worth bringing warm clothes for it...jacket, hat, gloves, etc. Just arrange transportation so you work within your time constaints. Just think how well everyone will sleep on the plane after that busy outdoor day.

Your timing looks quite tight. It will take you at least an hour just to get out of the airport from the time you land, together with making sure you get back in time for your flight, effectively you have 6-7 hours.
You do not say which day of the week you are arriving, but traffic is bad in Beijing most days. The rush hour times are particularly slow, if any of your options take you into the city you should plan for this.
Agree Mutianyu is reachable. The toboggan ride closes in rainy or icy weather. If you go to the Great Wall there won't be time to do anything else. Eating places around the gate of MuTianYu are touristy junky things, there is a Subways. However, getting to see the wall would be a great ending to your trip.

On alternatives : the Bird's Nest stadium in the Olympic area has artificial snow put in and around it in the winter. They have skiing/snow tubing.
Lakes freeze over, some have skating - Hou Hai lake is one that you might go to, rent some skates. Around the lake are a number of hutongs - traditional lanes with shops and eating places.
You will need to arrange transportation in advance, if you have a guide to take you around you can quickly visit TianAnMen, scoot inside the Forbidden City, see TianTan (Temple of Heaven)and have a good lunch.
Being outside will definitely require some cold weather gear, January is the coldest month, with the average temperature just above freezing. It's not damp in Beijing, but if the wind gets up you notice it a lot! - temperatures can feel blisteringly cold. (some days in January are -10C or below, together with a 30kph northerly wind this can feel a lot worse)

Just got back from Beijing and walking the Wall was a highlight. They had just had a rare Nov snow storm-parts of the wall (in the shade were icy). We had 3 hours on the wall- walked all 3 hours (with photo stops) . Wear layers- you will warm up from walking all the steps. It is a great way to use up some energy before a long flight home. Did the cable car up and luge down at Mutianyu. You can also take cable car down. Arrange for a driver and go- well worth it! It was a highlight of our trip to China.We did not have any traffic leaving or going to Beijing airport but we went at odd times of the day.

Good time of the day. There is not much traffic from the airport to Mutianyu as you are already out of town.

I Googled..Beijing airport to Great Wall ...and several tour companies came up. They do it in 3-4 hours. Looks very possible.u

This is fantastic! I didn't realize more people hadn't written in. Kids really want to try Great Wall, so looks like we will head there - and hopefully warm up walking the Wall. Am finding some tour guides now. Thanks to all for you help!