Lol I have a baby face and I'm 5'3" as well and people think I'm a 12 year old in the seventh grade... :/ Plus my parents look young for their age so I will forever look younger... my dad is three years away from being 60 and he hardly has any gray hairs and wrinkles and my mom looks the same when she had me 16 years ago and my sister is the same thing like you as well. It's like she grew to 17 and hasn't aged ever since. She is currently 26. So in other words, you are not alone.
You could try a new haircut. Especially if you have bangs. I don't know if you do, but they definitely make people look younger. Try adding some layers. Have some fun, and experiment with makeup to see what helps. Rounder faces can convey youth so maybe try contouring.