This was being discussed on The Wright Stuff this morning. The verdict of the panel was that it's ludicrous, for various reasons, among which were:-there's no way a child could be taken from its parents, there's only one exit, people should be entitled to go to parks on their own without being viewed as paedophiles, Ian Brady would not have been allowed in, but if he was with Myra Hindley he would, and the vast majority of child sexual abuse happens within the child's home.
Personally, I disagree with the rule.