My son is 3 1/2 years and i still don't leave him on his own. I have left once or twice to go to the cupboard just outside the bathroom and pick up a towel and straight back and he has hardly moved.
He has a bath about once a week, He is more into the Showers now and he usually jumps in with Dad or just after, if he wants one on his own.
But he usually wants a shower like twice a day, Must be hot for him.
I didn't overly like the baths for him either, cause he tries to swim like on Tv and gets a face full of water, Oh poor darling.
But nope, I still don't leave him alone.
Its way too dangerous.