Final answer:
Children start to recognize letters without understanding their meanings in the preoperational stage of cognitive development, which is from 2 to 7 years old.
Step-by-step explanation:
The stage at which a child begins to recognize letters but does not understand what they mean is the preoperational stage. During this stage, spanning from approximately 2 to 7 years old, children can use symbols to represent words, images, and ideas. Although they start to use language, their logic is based on their personal understanding of the world, and they do not yet grasp adult logic or the idea of conservation. At this stage, a child might not understand that the amount of something remains the same even if its appearance changes, which illustrates why they are only beginning to recognize letters without understanding their full implications or meanings.