i just fell off my bike today and broke my arm what can i do for fun?

Play hospital with any siblings. This could be a learning experience for them, to learn what it's like being in a hospital. You can tell them about broken bones but warn them to be careful.

Depending on which hand you write with you could draw or write a story. You could read, listen to music, dance, karaoke on Youtube, play games on your computer/tablet, ride your scooter, go to park swing and slide and many other things!