You may find that this gets you much farther in your request than whining to the adult. [substeps] Make sure to use your usual voice or even try a whisper if that helps you.
[header] How to be less whiny [title] Ask what you want in a polite, normal voice. [step] If your parents or other adults hear whining, they may often shut down with a firm " no " or even ignore you. Try asking whatever you want in your normal voice and make sure you're polite about it.