It's the bureaucracy
I think the problem with applying for a job to work with kids, or e.g. starting a sports club such as a martial arts club (which I have done in the past) is the amount of bureaucracy and the cost involved, not the belief that anyone is under suspicion. You have to get at least two adults through CRB. It takes a lot of time and money and there are a lot of other complex rules to follow, enought to put anyone off.
I am not sure how much bureaucracy is needed. Common sense combined with a willingness to confront any suspicious action or even suspicious traits is sufficient. For example, it was well known to all the adults in my local town that one of the school teachers was on some level a kiddy fiddler, but no one actually went down the line of confronting him until about 20 years after I left the school. However, everyone warned the children not to be alone with him at any time. I think this was wrongful inaction to some extent (the warnings were not specific enough e.g) , but otoh no amount of bureaucracy would have sorted the problem as no criminal record or specific allegations existed.
Informal interactions with kids are possibly a more difficult area but it's quite easy to signal a 'harmless' intention by simply making good use of personal body space i.e. interact with a child at a suitable distance .eg. about 5 foot to indicate lack of suspicious intention.
NOte, self defence tip, 5 - 8 foot is a good distance to interact with anyone to avoid conflict and help de-escalate the situation - should, for example, someone decide to confront you over an interaction with a child. It takes you out of immediate strike range, including knives, gives you room for any escape manouvres and also actually works to calm the person down because you are not perceived to be 'in their face'. It also helps telegraph any intention to attack i.e. at 5-8 ft the person has to make a strong deliberate effort to reach you which gives you time to respond. Also don't try logic in these situations, the person is emotionally high and needs to come down before they will listen to reason. Just ask them repeatedly (using different phrases) if they are calm, or ready to talk and meanwhile maintain the distance. If it's not working, run and put as many obstacles between you and them as possible.
Liked the camera one. Technically, the police officer also destroyed the evidence that you were 'wrongfully' using surveillance techniques to gather evidence. otoh maybe he or she thought that discretion was the better part of valour and that you were going to get your @$$ kicked if you insisted on pursuing the case - which would mean even more forms to fill out! I know I'd chicken out of that one for that reason. Why didn't you just shout or swear (from a suitable distance) at the kids, hopefully causing them to run and minimizing the damage? by taking a picture you were clearly signalling you were going to call the police and just inviting further hostility. Paris, because even she isn't as thick as you are.