Ryanair has been urged to review its procedures after a three-year-old girl fell from the top of aircraft boarding stairs, through a gap, onto the tarmac.
Olga Smart fell as her mother carried her 18-month-old brother and luggage at Stansted, in Essex, in July 2009.
The Air Accidents Investigation Branch report said Ryanair should ensure assistance was available to passengers with children and with special needs.
Ryanair said it had reviewed its procedures since the incident.
Olga was climbing the stairs unaided when she fell through a space between the handrail and the level platform at the top of the steps.
She was airlifted to hospital after receiving immediate medical help and was released 24 hours later.
The Air Accidents Investigation Branch (AAIB) report said: "The gap between the extendable handrail and the upper platform of the Boeing 737 airstairs represents a hazard to small children boarding or disembarking the aircraft."
The AAIB said there had been four similar incidents previously reported in the airline industry involving small children.
This had led to US aviation authorities taking action, including updating the Boeing 737 flight attendant manual.
The modifications proposed by Ryanair after last month's incident provided "only a limited physical protection against falling", the AAIB added.
The AAIB recommended that Ryanair review boarding and disembarkation procedures "so that assistance is made available to passengers accompanied by children and those with special needs".
Ryanair spokesman Daniel de Carvalho said: "New procedures including new high-visibility Tensabarriers, and specific announcements to passengers travelling with young children on both boarding and disembarkation, have been introduced in order to eliminate any recurrence of these extremely rare events."
In May, her mother, journalist Sasha Slater wrote about the incident in the London Evening Standard.
She described how Olga had "suddenly screamed and slid off the side of the platform," landing on her side on the tarmac.
Ms Slater went on: "I thrust Joe into the arms of an air hostess and ran down to reach my daughter who was lying, screaming, beneath the plane. I was forcibly prevented from holding her by one of the many doctors on the flight in case she'd broken her back.
"The next few hours passed in a blur of paramedics, sedatives, stretchers, helicopters and ambulances, brain scans and X-rays. But a day later she was running around in hospital, the only visible signs of injury some scuffing on her toes and knees, a sore neck, and an egg on her forehead."