Reviving this topic as we have had a few discussions at East Surrey N Gauge. In 2016 we added a paragraph to the constitution on safeguarding. My professional background was in running safeguarding partnerships, so I have some knowledge in the area, but not at the sharp end like @Calnefoxile, who makes some excellent points.
We will be updating the paragraph - other clubs are welcome to use if this is helpful:
"ESNG strictly complies with The Children Act 2004 and other relevant safeguarding legislation for all Junior Members. As it is impractical to have all members DBS checked the club stipulates that all children under the age of 18 or vulnerable adults must be accompanied by a close relative or guardian when attending or travelling to club meetings. This policy also applies for club exhibitions and where club layouts are invited to other exhibitions."
It is also important to apply common sense and ensure that younger or vulnerable members are never unsupervised, eg. they should not be be taken to the toilet except by parents/carers. I'm not aware of any incidents involving model railway clubs, but experience elsewhere has shown a need for vigilance.
It's a shame that the era of trust has perhaps gone, but historically there were those who grossly abused that trust, and there may be some who continue to want to do so.