In the new Earth's Children book, Land of Painted Caves, does Ayla somehow meet up with her son or the clan?

nope! but Danug shows up :) so there is like a little bit of her past coming back and theres closer with the whole mamutoi storyline

I haven't read it yet but from the message board postings and reviews I have seen I would guess no, that does not seem to be a part of the book. Unfortunately what I have seen is that many people were disappointed in the book, apparently it is very repetitive (which I've noticed in some of the other books as well) and left many loose ends considering it is supposed to be the final book. Some folks were even questioning if Jean Auel had actually written the book or if it had been ghost written. I probably will still read it, I've been following the series since the beginning but, honestly, after the first three books I think the series really went downhill.