She is now 17 and this came up in conversation the other night at dinner and brought the trauma back to me.
So dd1 was 3 and dd2 was about 5 or 6 months. She was a terrible sleeper and I was exhausted. I was out for the day with them at a local farm with children's attractions. I had been trying to get dd2 to sleep pushing her around in the pram for some time. She eventually fell asleep while we were waiting in the queue for a tractor ride that dd1 was keen to go on. Dd1 was nagging me about the ride and I had to make a quick decision. So I left dd2 asleep in her pram and took dd1 on the tractor. My (sleep deprived) brain thought I would be able to see the pram from the tractor. However the tractor went out of sight and for what seemed like an eternity I couldn't see dd2 in her pram 
We got back after 10 mins or so, dd2 was fine and still asleep.
But all these years later I feel awful. Someone could have easily have taken her 