The end of "Another Birthday": After spending his birthday feeling dejected and unwanted, the green pig with the birthday hat returns to the pig pen with the others at night, the lights go out, and then the piggies wish the birthday pig a happy birthday!
The end of "Cordon Bleugh", where the pigs discover that Matilda's cooking (which the other birds had turned down, finding it inedible and causing her to cry) is utterly delicious. The smile on Matilda's face is the cherry on the sundae!
"Joy to the Pigs" is also heartwarming, as Terence delivers presents to all of the pigs in the kingdom.
"The Portrait" from the Stella episodes features Willow forced to paint a portrait of Gale. During this time, she also helps out an artist pig who's making his own portrait. After Gale shows disgust for the pig's portrait and breaks the pig's paintbrush (leaving the poor guy in tears), Willow hands the pig her own paintbrush. The pig happily responds by giving her a small cuddle.