I was going to say something but to be honest Gacapa has said it so well....
"I know a reasonable number of men who don't have kids, but enjoy the company of their friends'/family's children. I'm sure most of us do. But if any of them told me they frequently hang around on their own at a local playground to play with strangers' children I'd be completely WTAF?!
I wouldn't care about any potentially "innocent" motives re. this bloke, OP. It's at best odd. And actually just bang out of order. He can go get CRB checked and do something official and supervised through the proper channels if he's that interested in interacting with children.
Any right thinking man, with consideration and awareness, would realise that this behaviour falls outside of appropriate boundaries."
And Budecah "Can we just clarify something here to pp who think he sounds normal : it’s NOT normal for childless, grown men to go to playgrounds to play with children."
Xihha I am so sorry to hear what happened to you. Thank you for telling us because it is important to remember what can happen.
ReanimatedSGB "She doesn't know if 'No, I don't have any children' means 'I am a weirdo'" - Not having kids doesn't make you a weirdo. Hanging around in a park without your own kids is weird. If a parent with kids went without them to hang around in a park, I would consider that weird too.
"or 'I am the brother of [another parent]" - I'd still feel suspicious of a man I didn't know at all playing with my kids,
"...or half way through my nursery worker training and getting some extra experience," Not sure how random unverifiable experience with kids in a park would count for anything,
"... or even I work in a care home and some of the kids are kids I am key worker for.'" Very few kids live in care homes in the UK (assuming this is the UK) and again that really would not be an excuse for me.
As someone else said, I'd expect someone who worked with kids to understand about safe guarding more than most!
"...a single parent of one of the DC and have given OP a stupid answer because he was fed up with being asked nosy questions." Then he is very, very stupid.
"... there really isn't one under every shrub." No one assumes there is, but I think we just want to do the best to ensure that people who have access to our children are safe, and this doesn't sound safe.