[engeljohnb]

There's tons, if you look up "[language] graded reader" or "[language] nature method."

Familia Romana by Hans Orberg is a great one for Latin. I frequently see people call it the gold standard for this kind of book, but they're all Latin enthusiasts, so they're not exactly unbiased.

[devilbunny]

Familia Romana is the first part of Lingua Latina Per Se Illustrata.

[Agingcoder]

I didn’t find that many - you can find graded readers, but very few ‘graded novels’ ( as in a full novel where chapters are progressively harder, not multiple independent tiny stories ) if I may say so