I really don't mind this sort of thing unless it becomes one-after-another, but I think a simple polite refusal or acceptance is the proper form. As for the appropriateness of the exercise, I think the form ("Hello my name is Joey I'm 7 I live in..." etc.) is a bit primitive, but the fact that real kids get to talk to real English speakers is good - all too many people in China have a nervous kind of feeling about 'foreigners' that is a result of bits of xenophobia in Han culture that stresses a 'They are REALLY DIFFERENT who knows what they'll do or say?' attitude, which often demonstrates or results in inappropriate this that or the other ('Welcome to China!' 'But I speak Chinese and have been here for 15 years.' Never mind, welcome to China!' etc. - after which it begins to be about face rather than real communication). Young kids, especially, can be talked to simply like real kids from anywhere, will respond to kindness even though it comes from a funny-looking guy whom they otherwise might be taught to fear as an ogre, and will be delighted. I really don't have much of a problem with this, unless, obviously, some parent simply uses you inconsiderately for a long period of time. The value of the exercise is not really in teaching method/learning more language, but in learning that people who look different and speak different languages are people too - as good a lesson as I know for people of any age, and a good one to acquire while young.