Have done 10 BA long haul sectors with our toddler in CW in last year. At 10 months, easy. Lots of sleep and room to share flat bed. At 15 months and walking, less easy as wanting to explore and a whole lot bigger/more active. For next trips at 20 months, I'm seriously considering an extra seat as last time I ended up sleeping on the 747 upper deck side locker! Endorse what has been said re the 2 rearward facing middle seats (rows 13 & 20 in 747). If flight isn't full, you'll find that anyone in the aisle seats relocates asap so you'll get a flatbed each, esp if you travel an on off peak day. Always go for night flights and try to limit to one sector a day. Our $100 investment in a portable DVD player also worked wonders.If you do manage to travel over second b/day, remember that BA gives a complimentary seat for the subsequent sectors at infant fare - very generous.

Infinite Cycle - you've lost me on that, I'm afraid. How is expanding into an adjacent empty seat in your own cabin a problem? No different from the ability in 3 abreast economy to raise the armrests & spread out if lucky enough to get an empty row (if fitted with the increasingly rare moveable armrests). Not at all comparable with moving to a higher class cabin. BA cabin staff have always been more than happy if it adds to the chances of a quiet night!