I took DS (then 6 or 7) to London for the day (we live in the home counties) and switched from the overground to walk down the road to the tube station.
As we approached the tube we heard a lot of noise and I clocked the police van outside. We got to the entrance only to see two policemen holding a bloke on the floor whilst several others stood around with their nightsticks out ready. They hauled him up and matched him to the van, lots of yelling. As they locked him in and it got quieter, DS loudly announced "That was SO COOL! I've never seen anyone get arrested before! I LOVE London!"
The police were trying to remain serious, but a couple of them couldn't manage and started really laughing. One thanked us for lightening the situation for him and was glad DS enjoyed the show and hoped he felt safer now?" DS was very positive about police after that.
Another time a bloke stepped off a packed commuter train and another bloke came up behind him, grabbed his arm and twisted it up husband back and said "Ahhh, Mr Borrocks, I've been waiting for you. If you'd like to come with me, we have a few questions to ask." The other bloke was calling him as 'bastard' as he got marched out.
The bloke getting 'arrested' was my DF and the 'bastard' was his best mate, pranking him. I never witnessed that as I was a child at home in bed, but plenty did, and my DF and his friend still tell the story.