When Mary Margaret says that she wants to have another child, it was to accommodate Ginnifer Goodwin's real-life pregnancy with her first son.
Prince Eric mentions his intention to travel to Agrabah, the fictional setting of another Disney classic, Aladdin (1992).
The bone handled, three tined, dark grungy metal "salad fork" was a standard item before industrial metal stamping was developed. Untill the late 1800s all forks were made by blacksmiths. That means each tine had to be hammered out by hand; two tines was easy, three was tricky, four or more tines was really, really hard. And no one had stainless steel.
When Regina is pretending to be Ursula and is speaking to Ariel, she refers to Ariel as "my dear sweet child." This line is a reference to the song "Poor Unforunate Souls" in The Little Mermaid (1989). Also, at the end of her speech she says that Ariel could be "part of Eric's world," a reference to the song "Part of Your World" from the same movie.
When Snow and Ariel enter the ball, the embellishments on Snow's dress form a hidden Mickey.