The pilots of two aircraft that collided mid-air with disabled children on board were probably distracted by their passengers, a report finds.
One of the pilots involved said he saw an aircraft "converging" on his own before losing sight of it in June 2019.
A child passenger who was unsettled prior to take-off became vocal during the charity flight causing the pilot to cut short the trip, investigators said.
The other pilot said he felt a "bump" but had thought it was an air pocket.
Although no-one was hurt, investigators from the Air Accidents Investigation Branch (AAIB) said the case "highlights the importance of avoiding distractions".
Child passenger 'unsettled'
The pilot of a Cessna 172R Skyhawk had been transporting two disabled children and a carer at the time.
During the charity flight at White Waltham Airfield, near Maidenhead, Berkshire, on 23 June 2019 one of the children became "verbally and physically unsettled" before takeoff "but was then reassured by his carer", the report found.
The aircraft took off at 09:52 BST but mid-way through the flight the previously unsettled child became "vocal" so the pilot cut the route short by flying towards Henley-on-Thames in Oxfordshire.
The pilot said he saw a "bright red aircraft above...converging on his aircraft" and lost sight of it before it reappeared briefly.
Event organisation criticised
The other aircraft involved in the accident, a Fuji FA-200-180 Aero Subaru, was also carrying a disabled child and their carer.
Damage to the Cessna's right wingtip was only noticed when both pilots had completed subsequent flights without incident, the report said.
Another pilot, who was not involved in the accident, told the AAIB that the event was "not as well organised as usual and that not all the pilots that flew were at the briefing".
The report concluded it was "likely that both pilots were somewhat engaged with their passengers, which probably affected their lookout".
The airfield said it would conduct risk assessments before future events.