How was the man with the red eyes talking to the children?

The man with the red eyes talked to the children through their minds.

“I have been waiting for you, my dears,” the man said. His voice was kind and gentle, not at all the cold and frightening voice Meg had expected. It took her a moment to realize that though the voice came from the man, he had not opened his mouth or moved his lips at all, that no real words had been spoken to fall upon her ears, that he had somehow communicated directly into their brains."