When I was a child my parents always made sure we attended Sunday School. These schools were first set up in the 1700s in England to educate working children.
That's interesting.  Did Sunday School only teach religion or did it cover other school material?
It's aim was to cover the Bible, plus reading, writing and arithmetic.
Are Sunday Schools associated with a particular religion?
The movement itself was cross-denominational. Today, each church tends to have its own Sunday School
Is there a particular curriculum that most Sunday Schools use?  Like lesson plans.
I believe there are lesson plans. There certainly were when I attended and we were expected to study!
Nice. Are Sunday School teachers certified in some way?
I don't think so, but they must certainly have a knowledge of the bible. Imagine, back in the 1700s there were 5,00 schools in one city alone, so there must have been some formal education.