Ryanair has introduced new procedures after a young child fell onto the concrete while boarding a plane at Stansted Airport in England in July 2009.
The three-year-old girl slipped through the gap between the handrail and the platform at the top of the steps, which she had climbed unassisted.
After receiving initial medical assistance, the young girl was airlifted to hospital, but was released 24 hours later.
The Air Accidents Investigation Branch (AAIB) recommended that Ryanair review its current passenger boarding and disembarkation procedures.
It said that assistance should be 'made available to passengers accompanied by children and those with special needs'.
The 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.'
Ryanair said: 'New procedures including new high visibility tensa barriers and specific announcements to passengers travelling with young children on both boarding and disembarkation have also been introduced in order to eliminate any recurrence of these extremely rare events in the context of over one million Ryanair flights over the past two years.'
The AAIB said there were four previously-reported similar incidents on Boeing 737s involving small children.
This led to US aviation authorities issuing a special airworthiness information bulletin, the amendment of the Boeing 737 flight attendant manual and the release of two special safety bulletins.
The AAIB said it was making the safety recommendation to Boeing about the airstairs design as the special bulletins 'do not provide physical protection against a child falling through the gap'.