Looking on the internet deeply has found these results:

on the playground is the most popular phrase on the web.

at the playground 113,800,000 results on the web	on the playground 121,300,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
'Cause if she was at the playground... We'll be at the playground drinking beer. It was an accident at the playground. Anyway, we're all meeting at the playground at 8:00 and heading out, if you want to join. We're at the playground, Brian. Katy told me what happened at the playground. I just saw the Greek at the playground. And Aiden said at the playground That he smelled beer on Kelly.	You're like some hurt little girl on the playground. The youngest visitors can enjoy on the playground or in animation program. There's a tunnel on the playground. She fell down on the playground, that's all... You can catch up with the other kids on the playground. He's hurt himself on the playground. Last punch I took was on the playground in second grade. You can spend pleasant hours playing miniature golf on the playground at Prati di Vizze.

at the playground

113,800,000 results on the web

on the playground

121,300,000 results on the web

More popular!

'Cause if she was at the playground...
We'll be at the playground drinking beer.
It was an accident at the playground.
Anyway, we're all meeting at the playground at 8:00 and heading out, if you want to join.
We're at the playground, Brian.
Katy told me what happened at the playground.
I just saw the Greek at the playground.
And Aiden said at the playground That he smelled beer on Kelly.

You're like some hurt little girl on the playground.
The youngest visitors can enjoy on the playground or in animation program.
There's a tunnel on the playground.
She fell down on the playground, that's all...
You can catch up with the other kids on the playground.
He's hurt himself on the playground.
Last punch I took was on the playground in second grade.
You can spend pleasant hours playing miniature golf on the playground at Prati di Vizze.