A steady beat is a primary music fundamental that all musicians must master. A good working definition of a steady beat is a constant, continuous pulse. The best way to understand a steady beat is to experience it! It can be experienced through large motor movement; preschoolers could walk, run, hop, march and skip to the steady beat. As children age, you might want to expand the steady beat experience by using body percussion (clapping, patting, snapping or stamping) or non-pitched instruments (drums, shakers, sticks or scrapers).
It's a plus to read a storybook to the steady beat as the children respond to the beat. Two favorites are: Crocodile Beat by Gail Jorgensen and Patricia Mullins, Bradbury Press ad Old Black Fly by Jim Aylesworth, Henry Holt & Company.