Sarah OReilly, from Bedford Road in Hitchin, was at a toddler's morning at the Angels Reply pub, also in Bedford Road, with her daughters Sienna, aged three, Skye, aged four, and son Connor, four months, when Sienna went missing.
Staff and other parents were alerted and immediately began searching the area. The police were also called and 10 officers arrived and joined the search.
Mrs O'Reilly said: "We went over to the Angel to have a coffee and a chat with the other mums. I suddenly realised Sienna was missing and everyone began looking for her. We found her after half-an-hour hiding behind the fruit machine.
"When she came out she had a Christmas bauble, a cutlery knife and some leaves and asked if she could have her lunch. I just picked her up and put my arms around her. She was obviously having a lovely old time behind there and probably couldn't hear us because of the noise of the fruit machine."
"Fruit machines are attractive to children and she did find a pound behind there a few weeks ago."
"The staff and everyone at the Angel's Reply were spot on and the police arrived within five minutes and were fantastic. Everyone had a go at the pub, and the police too, but I just wanted to say thank you."
A police spokesman said: "Incidents of this nature are taken extremely seriously. Officers were deployed to the scene within minutes and thankfully the child was found safe and well. Our priority is for the child to be found and reunited with its parents."
