Did the children summon a spirit with their chants?

I'm babysitting five children right now. A couple of minutes ago they were all sitting quietly and giving me no trouble. They barely said a word. Then suddenly they all stood up, held hands, and chanted, "Hail, hail, fire and snow. Call the angel, we will go. Far away, for to see, friendly Angel come to me." Then they sat down again. Almost immediately, all of the glass in the china cabinet began to rattle. Was it just a coincidence, or should I be concerned? I wouldn't have thought anything of it, but I discovered a pentagram on the wall of their parents' bedroom just now. What should I do?