Some issues with this bike. First, the kid managed to somehow take the rear derailleur apart. He's been complaining about a skipping chain for a few days, but before I could get to it and check it over, he came to tell that it's broken. And it was - one of the jokey wheels went missing. I found a replacement, put it all together, not forgetting to locktite the bolt, but then another issue came up - the rear shifter is not working. It's the one I didn't take apart, limiting myself to just flushing it with WD-40. I can now only get a single click out of it. I guess I'll be taking it apart after all.