After such a long hiatus, it's probably a good thing that this episode was relatively stand-alone in nature. There were definite connections to the larger mythology, particularly in terms of the child at the center of the story, but this was mostly a chance to reconnect with the characters and the series as a whole. On that level, it definitely succeeded.
I'm not sure that the already devoted fans missed the visual clues that the child was connected in some way with The Observer. The most obvious conclusion is that the child was from the same species as The Observer, so to speak. In turn, The Observer is likely a member of the version of humanity that comes from the supposed parallel reality that Mr. Jones described. (The fact that Mr. Jones was speaking from belief in a document that Walter wrote, once upon a time, lends considerable doubt to all of it, of course.)
If that's true, and the child is from this other reality, then it might explain his apparent empathic abilities. Empathy doesn't quite explain all of his talents, however. It doesn't explain how he managed to "receive" the information related to Olivia's case. That's not empathy, and it's not quite psychic ability, either. But it does match up fairly well with the notion that The Observer, and perhaps his kind, can sense when and where something related to The Pattern is happening.
The child's connection to Olivia may also be related to her supposedly "special" nature. The child managed to connect with certain individuals when necessary, but he seemed to have a stronger and deeper connection with Olivia. I may be reading into that more than I should, since it could be a matter of time and proximity, but now that there's a hint that Olivia is different from everyone else, it's hard not to consider such possibilities.
As I mentioned, this was a good episode to use as the beginning of the season's final run because it was a strong re-introduction. Walter got to show his quirky, mental side, as well as his scientific creativity. Peter's jaded past provided a key clue, and he tossed out several great barbs at his father. Beyond the core Fringe Division team, Olivia's relationship with her family informed her relationship with the child, and her interaction with Charlie and Broyles served as a reminder of her professional support system.
Because most of the connections to the mythology were either implied or left to the end of the episode, this succeeded on reminding the audience why the show works on a fundamental level. It's still relatively accessible, and it hasn't yet become mandatory to understand the mythology to understand what's happening in an episode. Considering how this season has come in fits and starts, it's a smart move to keep things as simple as possible while still giving the junkies new information to ponder.