While waiting, he wandered into an empty train and fell asleep, only to awaken with the train in motion, hurtling him far away from home.
Terminating more than 1,500 miles away in Kolkata - a strange, frantic city, whose language he didn't speak - Saroo is lost in a seemingly hopeless situation.
The film throws light on the sensitive issues around adoption and the motivations of parents who adopt children from different countries and cultures to their own.
All the while, Saroo's relationship with Mantosh becomes increasingly strained - not helped by not knowing what became of Guddu.
Narrowly avoiding being kidnapped, and with no paper trail or family name, he ended up in a local orphanage, from where he was eventually adopted by a couple in Australia, starting a new life on another continent. Opening with the little boy's alarming journey into the dangerous melee of Kolkata, the first act immerses you in Saroo's experience.
Alone and bewildered, the camera stays close to him, following him up and down the train as he screams for help.
Until, that is, at a party, when the smell of freshly made Jalebi - an Indian sweet - triggers old memories.
This leads to a discussion of family and identity that comes to govern Saroo's journey throughout the rest of the film.
Deposited in Kolkata, the camera then draws out, revealing his small, vulnerable body set agains the huge crowds and unfamiliar landscapes of the big city.
Overlooked and unable to ask for help (Saroo speaks Hindi, while the language in Kolkata is Bengali) he is destined to become one of the many street urchins that inhabit the city's alleyways and archways.