i did something similar in elementary school! I might have been trespassing as well at the time but i didn't really know any better (kind of)
So there was a sort of community center next to our school and in it's rear was this playground. I'd somehow managed to miss my school bus but hadn't realized and figured I'd go playing there since standing around was boring and I'd always wanted to see it anyways. Since there was a shed near the fence that was short enough to be climbed I hopped onto it's roof then over the fence into the playground (I should consider myself lucky it was a sand flooring rather than wood chips).
While I'm inside (surprisingly not found/noticed by anyone) I'm jogging around and decide to check out the monkey bars. I've never climbed them before and thought I'd give them a look. Instead I fall headlong into one of the overhead bars, it being taller than I stood especially on a mound of sand. Wasn't until I bothered to check the dripping from my head that I realized I'd cut my head on the thing and was bleeding.
To make a long story short though I got patched up and after some disciplining never bothered with that place or missed my bus again