I think the "And I've had so many friends" line by Glinda is supposed to be funny. Certainly the way it was delivered when I saw the show was hilarious, and the audience laughter was appropriate and expected. But then the "but only one that mattered" line that follows is supposed to put a lump in your throat. When I saw it, the "so many friends" line was clearly separated by a pause from the "only one that mattered" line, so that the appropriate response for each part could come. If the two parts are running into each other, I can see how it becomes a "why is everyone laughing" moment.
I think the baby being green is amusing because of the over-the-top melodramatic staging, with the big chords and the raising of the baby.
"What was the name of that cheese that I like?"
"you can't run away forever...but there's nothing wrong with getting a good head start"
"well I hope and I pray, that maybe someday, you'll walk in the room with my heart"
