The Stranger Things star celebrated her 16 birthday on 19 February and used the milestone to hit out at those who have made "inappropriate comments" about her since she shot to fame playing Eleven on the Netflix series when she was just 12 years old.
"16 has felt like a long time coming. I feel like change needs to happen for not only [in] this generation but the next. Our world needs kindness and support in order for us children to grow and succeed. The last few years haven't been easy, I'll admit that," writes Millie in an Instagram post.
"There are moments I get frustrated from the inaccuracy, inappropriate comments, sexualisation, and unnecessary insults that ultimately have resulted in pain and insecurity for me. But not ever will I be defeated. I'll continue doing what I love and spreading the message in order to make change. Let's focus on what needs changing and I hope this video informs you on the things that go on behind the scenes of the headlines and flashing lights. Don't worry, I'll always find a way to smile. Leggo 16."
Millie recently said growing up in the spotlight has been difficult for her at times because she doesn't think fame is "normal".
Despite this, the actress has had many achievements in her young career.
In 2018, she was announced as the youngest-ever Unicef Goodwill ambassador, she was appointed on World Children’s Day.
When she was 13 years old she became the youngest Emmy nominee in history, being recognised in the Best Drama Supporting Actress category for playing Eleven on Stranger Things.
She's had brand collaborations with a number of notable brands including Converse for sneaker collections, a Pandora jewellery line and Vogue Eyewear.
The latest mega career move from Millie is her skincare brand, Florence by Mills.
Compile by Phelokazi Mbude