There are quite a few of them -- many are aimed at the 8-12 age range, but a few are intended for younger kids. These are ones I've gleaned from various searches. There are also series of books about individual religions - so one about Buddhism, Islam, Christianity, Hinduism, Judiasm, etc. Libraries have a section (200s in the Dewey Decimal System if you care) that you could browse.
I'm cutting and pasting Amazon's description - they say grades 4-6, but we read this with our 3, 6 and 7 year olds and they loved it. It answered a lot of questions for them - a very balanced and non-judgemental book. Excellent - we loved it.
Gr 4-6-- A provocative look at the concept of God that differs greatly from the Judeo-Christian idea of God as a person rather than as a vacuous feeling or entity. Major world religions are introduced in combination with the well-known teachers representing them (Moses, Jesus, Buddha, Mohammed), and whose words evolved into a library of Holy Books: the Bible, the Torah, the Koran, the Sutras, and the Vedas. Similarities are drawn among these faiths, showing common strands of truth and prayer as a universal tool of communication with God. Brief discussion is given to those believing in multiple gods as well as to those who experience religious persecution. Boritzer's attempt to synthesize and make accessible the many concepts of God results in the New Age concept/belief of pantheism. Marantz' Henrik Drescher-like illustrations are bold and bright watercolors, occupying full pages that face the poetic free-verse text. At times they serve a somewhat decorative purpose, but usually expand and elucidate elements in the narrative. The reasoning process used throughout may occasionally prove too abstract for many children, making this a picture book for older readers. It will be best utilized by religious-education teachers and parents. --Celia A. Huffman, Cuyahoga County Public Library, Cleveland
~~ Natalie ~~ Loving and learning with my DH since 09/1992 , DS1 03/2002, DD 06/2003 and DS2 09/2006