Why was Jany Eyre (in the novel) treated so badly?

Yes, Mrs. Reed thinks of Jane as a burden. Her children then treat Jane badly because they CAN. Their mother has given them the right to treat Jane badly because she treats the girl badly. Also, I think in the 19th century people were more inclined to think of children as cruel. Kids can certainly be cruel, but in the 19th century writers would often have children being cruel to each other without really explaining it. Though I think Charlotte Bronte implies that the Reed children are selfish and resent Jane's presence in the house, too.