This picture to me, is worth a thousand words on how to teach Fractions to elementary students.
As you can see, this is a photo from a book which is fabulous. It is called Elementary Middle School Mathematics, Teaching Developmentally by John A Van de Walle, Karen S. Karp and Jennifer Bay-Williams.  This is from Chapter 16 about Fractions in the eighth edition. This book is the best source I have found for teaching mathematics to elementary school children and is my textbook at Cal State Northridge for teaching Elementary Math.  For teachers and tutors and parents, you can obtain it on Amazon or eBay or other book sources. It is published by Pearson.
Pose these kinds of problems to your students and math will become a pleasant, magical, fun experience.
You can see the problem is well defined such as
Find 1/3  of  3/4 of the pizza which is 1/3  x  3/4 = 1/3 of the 3/4 is 1/4 of the original pizza = 1/3 x 3/4 = 1/4

Walle text Elementary Middle School Mathematics – Teaching Developmentally