Two women pictured walking along a railway line with a pushchair have been branded "totally irresponsible".
The pair were seen with a young child on the the Keighley & Worth Valley Railway (KWVR) heritage line on Sunday.
Staff said the heritage line, which was used to film the 1970 classic The Railway Children, was still used "intensively" for training runs.
A local MP said encouraging children to walk on the tracks was "dangerous, risky and totally irresponsible".
KWVR operations manager Noel Hartley said trespassing had increased during the last year due to false assumptions the line was not being used.
"It's incredibly frustrating and disheartening to see people blindly carrying on doing it regardless of the risks involved," he said.
"We have been running engineering trains throughout all of this."
While passenger services were currently suspended, Mr Hartley said engines had been passing every 40 minutes during the past week.
Keighley's Conservative MP Robbie Moore, who shared the image taken on Sunday afternoon, said: "Trespassing on the railway is illegal and dangerous - please stay safe and do not do it."
Mr Hartley added: "We've had people taking photos of others doing handstands on the rails last summer, a dog-walking business taking dogs for a walk.
"But it's taking kids for a walk on the railway which is really silly - it starts to instil the idea in children that it's OK to trespass on the railway property."
The line reopens to passengers on 17 April.