Visitors said they saw the escaped chimps emerge from the bushes on to a path, as others sat on top of their enclosure wall.
McFaul can be heard in the video warning the children to stay back.
A visitor to the zoo caught footage of the breakout and posted it on social media.
But the chimp ignored their commands and sauntered across the road.
Other chimpanzees were filmed sitting atop the walls.
She said she was "scared" but called it an "amazing" experience and said the chimp appeared to be "very calm".
Danielle Monaghan, who was at the zoo with her two children, partner and his young nieces, expressed concern about safety.
Belfast City Council, which runs the zoo, said: 'Zookeepers were present as the chimpanzee quickly returned from an adjacent wall to the rest of the group inside the enclosure'.
No white flag for Day at wet Pebble Beach
Jordan Spieth , the 2017 champion , was at 10 under through 16 holes when play was suspended for the day due to heavy rain. That makes Mickelson's up-and-down day which featured four bogeys, four birdies and an eagle much more palatable.
We also know from said trilogy that most of the apes are reasonable but are just afraid to trust humans and rightfully so, we're the worst.
"It may have been a different story if it had been aggressive but it absolutely wasn't". "We may have to remove the trees or make them a smaller level, although we don't want to do that". "We just walked past it and it was absolutely grand".
Zoo manager Alyn Cairns told the BBC that they believed that recent storms had weakened a tree in their enclosure, allowing them to snap off branches and construct the ladder.
Families described their shock at coming across a chimpanzee on one of the zoo's paths.
Green party leader Clare Bailey told the BBC: "We need to really start looking at what's going on at Belfast Zoo".
"We like things to be natural in their enclosure, to have trees in it, but we will review it".
The animals were locked into their inner enclosure after the adventurous ape returned.
A Red Panda is pictured at the "Zoom Torino" a zoological park in Cumiana near Turin, on June 3, 2015.
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