Toddlers can get into all kinds of scraps so I had to write a post about toddler safety. I feel like they need to be supervised at all times. I would be fearful about unsupervised toddlers as they are constantly exploring and have no real concept of danger yet like sticking their fingers into electrical sockets or sprinting without observing a step or strewn toys in front of them.
My sister had a major accident as a toddler as she fell headfirst on the concrete floor from her tricycle that was caught on a step. She still has a scar decades later and I still recall the bloody towel.