It`s not policed me and my 18 year old daughter have used each others tickets by mistake a few times, the stewards never look at the lights
It is policed so it's not a case of "never". Myself and someone else on this thread have already indicated that we've seen it.
So maybe it's "rarely policed". Maybe you just got lucky. Maybe the steward(s) in question when you entered realised you were with your daughter, noticed she had an adult light and you had a child light and just used common sense.
Regardless it's not "never".
And I know the club have briefed stewards to be more vigilant on this.