Please Help, Kids Untrained My Dog

So... I had JUST finished teaching my dog to roll over. She knew sit, shake, lay down, and roll over. Then these children started living at my house (ages 4-6), and they started to 'train' my dog when I was not looking. I would come into the room and they would have a bag of treats in their hands, telling my dog commands and rewarding her when she was not doing the commands, and not doing the right tricks. Now, when I tell her to sit, she lays down, when I tell her to lay down, she plays dead, etc, etc. How do I fix this? It has been months now, and I am just about ready to give up all together on her. Please help!!! ;(