Yes I have went to the park and played in just my diaper and shirt.
This was when I was about 12 years old.
The park in our town was a small town park and pretty secluded and it was a few blocks down from my house.
So one night I put a diaper on which I believe was a plastic backed pampers diaper and put my shorts on and shirt and shoes and then road my bike down to the park.
I then went into the park which was lit up with lights and took my shorts off and left my shoes and shirt on.
Then I went on the swings, slide and even those spring rocking horses which was fun.
I also went on the merry go round and climbed up the stairs to the long slide the park had and went down the slide in my diaper, shirt and shoes probably a thousand times and played some more for a few hours or so and then put my shorts back on and went back home.
I did that a few times more and it was fun.
However now I would not do it as a lot of parks have video cameras for security so I would not want to get on video camera doing that especially as an adult.