Yes, twice, in 2000 and in 2002. We were in Shanghai and Bejing.
We took our kids in 2000. They were 8 and 4 at the time, and did great!
China has become much, much more 'westernized' in the last few years . . . you can find McDonalds, Pizza Hut, KFC, etc. just about anywhere, if you want. But I would really encourage you to try the local cuisine . . . it's a chance to try things that you won't get anywhere else in the world!!! (And no, I am NOT talking about eating cats and dogs, either, as some people around here think that's all Chinese people eat

)
If you have allergies, bring your meds. I'll warn you; the air quality is very bad in the bigger cities (Shanghai and Beijing). China does not have air quality and polution control standards that we have here. Be prepared for wheezing and buring eyes.
Also, be ready for huge masses of people everywhere. Think of lower Manhattan in rush hour . . . then multiply that by 10. All the time. It is just amazing how many people there are there!!!
But yes, for the most part, everyone is friendly and gracious. However, being an emerging country, you probably will see lots of peddlers, who can be aggressive sometimes. Just smile and keep saying NO and shaking your head. Even with that, there is little crime, such as pickpockets or muggings . . . but you should exercise general tourist caution.
And finally, if you go to any markets, you WILL have to barter. That is an art form. You can generally knock off 1/3 to 1/2 of the asking price. The trick is to offer about half or less of what they want, then go back and forth. It is helpful to say things like "I can get this for half of what you want from that guy over there!!" After a while, you and the merchant can settle on a mutually agreeable price. And it takes twice as long to go shopping there, because of this.
Have fun!!!!