Engagement entails much more than rote repetition of a procedure. Math worksheets tend to present very similar problem types over and over, leading to mundane practice of disassociated skills. For students who understand the material and successfully complete an assignment, another worksheet becomes meaningless. On the other hand, for the students who don't understand the material, an alternative method of instruction is what's needed. Another worksheet simply adds to the student's frustration, or worse, contributes to a belief that "I'll never understand math." A cute image or a "fill_in_the_blanks" riddle does nothing to increase engagement or learning (and let's face it, those riddles are not funny!). Instead, teachers need to increase engagement by providing students with exercises in which they discover patterns and relationships, solve problems, or think creatively about math relationships.
There are some new materials being developed now based on what we are learning about how the brain learns. These brain_friendly materials should be an improvement over what has existed. I recently bought a book by Marcia L. Tate titled "Mathematics Worksheets Don't Grow Dendrites." I highly recommend her book. She gives a great deal of information on alternative activities that are better for your child's brain development and for learning.