These books (The Magic Tree House Series) are ideal for about 5 - 8 year olds. They're full of illustrations and basic facts about the period to which Jack and Annie get transported.
Jack and Annie go to ancient Egypt and inside the pyramid of a queen. They help the ghost of said queen to find her Book of the Dead and thus complete her trip to the underworld. Also, a cat helps them out when the get lost in the maze of the pyramid in this, the third in the series.