I went on a search to find the best ways and resources for teaching rhythm to elementary school children, here is what I found!
This website goes through a basic lesson plan teaching children rhythm by using common words to represent different kinds of notes and beats. This is a great way of developing a sense of rhythm for children.
This blog is a basic set up to teach children about rhythm with their heart beat. It teaches children what rhythm is and uses cut out hearts and straws to practice beats and rhythms.
This is a nice resource where you can print out rhythm sheets that you attach to a clothesline and go over in class. Each note is represented by color and the length of note is represented in the length of the paper.
This youtube video shows a great way to incorporate rhythm into learning about each student in the class. It allows for each student to pat a steady beat and internalize rhythm.
These are great rhythm worksheets that asses the students to see if they understand the material. Basic rhythms and note lengths are given for students to understand note lengths.