How do I introduce Allah to a young child in a pleasant way, not a frightening one?

A child's first introduction to Allah should be full of love and a sense of safety, so that they love Him before they fear. Begin by speaking of Allah as the loving Creator who gives every blessing they enjoy, such as their mother, food and the sun. Point out the signs of Allah's greatness in nature when playing outside. The Prophet ﷺ said: “Indeed, gentleness is not found in anything except that it adorns it” (Sahih Muslim, Book of Righteousness, Joining Ties of Kinship and Manners), so teach gently, not by frightening them about Hell. Answer their questions honestly and briefly according to their age. Make mentioning Allah's name something pleasant in the daily routine. See educating the family.