When I read to children, I try to become the characters. It's great if you can make a separate voice for each character. Sometimes you can lower your voice with excitement or get more intimate about it: you can lean forward and engage the children as a narrator or as a reader. It's particularly important that you find the voice that you want to use for each character, because then children can imagine that person as you're reading aloud. And of course, the illustrations help enormously.