Is it common to call other people "sweetheart" instead of their names?

Native speaker’s answer
Rebecca
Sometimes. Some older people may like to use words such as "honey," "sweetheart," or "dear" to address someone younger, like an elderly woman to a child. It is usually meant in a friendly way, but can be considered condescending depending on the context (you can pick up clues from the conversation or tone of voice). Ex: Oh, sweetheart, thanks for the gift. Grandma loves it! (Loving, friendly tone) Ex: Sweetheart, you made a mistake here. Can't you do it properly? (Condescending tone)