Perhaps those of you with twins should get a campaign going. Be sure to report this to the airlines when it does happen. Point out that it wastes their staff's time and energy reseating parents with two lap babies when this could easily be written into the reservations program.

If you are seated in a row with only two seats, you may want to rebook just as precaution. Call the airline, see if they can tell you about the O2 masks and if not, move to a row with three or more seats just to be sure.

P.S. CD WOW, we have discussed the fact that one parent sometimes is not allowed to fly with two children under a certain age, even if another seat is purchased but it wasn't relevant to the OP's question, as both parents will be flying.