I had three or four experiences with infants and very young children in December. On one redeye flight I was in F on a 737, with a crying infant in the second row of Y behind me. I was annoyed at first, but then I had a scotch and the engines started - within 10 minutes s/he was background noise. On another flight in Y a four-year-old howled. When the seatbelt light went off her mother took her back to the rear galley/lav area and kept her there until she quieted. I also saw 5 or 6 infants and small children in Y and C on various flights who were no worse than the rest of the pax and whose presence I quickly forgot about.
Next month I am taking my 2-1/2 year old son on his first flight (pessimists: avoid UA 2833 PDX-LAX-PSP on February 9). I have no idea how he will react, but I think he'll be fine -- because I've told him in advance what he'll see on his first flight.
How have other parents prepared children for their first flight?