You are so right playfelt. There is nothing to feel guilty about if you have to raise your voice and let the children know you have reached your limit and you mean business. I agree that if you use a firm work like 'enough' or 'listen now' or sometimes I do a double hand clap to get my group's attention. The double hand clap works well outside at a park too when they really cannot hear my voice. They know it's me and they all stop and look at me for the next instruction.