Both my girls were down to one nap by 12 months. I find the transition period between two and one nap can be tricky, there seems to be a period of time when 2 naps is too much and 1 is not enough and nothing works well and you end up with a child falling asleep in their high chair at lunch because 'tired' and 'hungry' happen all at the same time! There is a kind of limbo twilight zone between the 2 stages LOL. Although DD2 has been one nap for over 4 months now if she has a crappy night she will be back into limbo twilight zone and things just don't work well until she catches up, so I don't think we've entirely finished the transition. With DD1 I remember what worked some days was if we were out in the car and she fell asleep for 10 or so minutes it seemed to be enough just to keep her going until after lunch until she had a proper sleep, and gradually over time she became less reliant on the little morning cat nap. but it just tided us over until she could properly get to one nap.