I lost my ds1 at Oxford train station when he was four. I'd been to Birmingham having been offered a job there and taken son to see new school. At the barrier, I looked down to look for the ticket in my purse and let go his hand for literally a minute. Looked up, he was gone. I thought he was teasing around, so called out for him jokingly. No response, GONE.
To cut a long story short, he was reclaimed after 30 minutes! By which time, station staff had searched, passengers been questioned as to whether they'd seen a small blond boy, police called by station staff.
Just as the police officer was asking me "what is your son wearing?", a distraught young Australian woman arrived with my ds1 sobbing in tow.
She and I had waist length blonde hair and the same distinctive red and white coat. He had followed her, not me, and got as far as the traffic lights by the opium den (not far from station but a few minutes walk) when she stopped for the lights.
She looked down, he looked up and wailed "You're not my mummy!"
Thank God she had the prescence of mind to ask him "Where is Mummy? And what's your name?" And brought him back.
Reader, I kissed her. ( and if you're reading eight years later gap year girl, thank you so much!) .
So I sympathise, op, and ds2, as soon as he can walk, will have reins....