It’s conditionally taxed income - if it’s expected that you will owe over $1000 in taxes as a dependent, you’ll need to file a 1040-ES and keep up with quarterly tax payments. If you make less than $400, the IRS does not care, and that is probably a sum outside the scope of earnings for many (if not all) childhood lemonade stands.

And you better have a permit, or the local Karen chapter will have a word: https://youtu.be/FRLL-w9sKdg

The FDA would probably also like to have a word.