It might be a cultural thing, in China at least, to come across so very friendly and enthusiastically; I'm sure I remember this in Beijing in 2004.
But I would caution that you maintain "professional distance" (or "arm's length") from all labs; at the moment obviously things are going very well for you, but what happens if things do not go so well; you, as well as they, get upset?

You have to adopt a professional, discretionary stance and realise amongst all probabilities, nobody is perfect, mistakes will happens, neglect can creap in, lack of responsibility for a job, scratched negatives (maybe even "accidentally cut") negatives... It could all happen at this lab, maybe a lot more. I don't regard kids "passionate about film" as being any more careful or reliable than a professional of 20 years' experience: they are still human!

At a minimum, you could allow them to use two or three images and wait for them to appear on the web where you can appraise their work. The copyright of the images is owned by you unless formally re-assigned. I think it is foolhardy to agree to handing over all your images for use. You do have to maintain some sense of proprietary and self-preservation: you never know what could happen.

None of my films were processed in China; they were all express posted back hom from a stopover in Hong Kong.