Worksheets will help, but showing cubes of odd and even numbers helps them understand. For example, show one cube. Can you make 2 even or equal groups? No so it is an odd number. Show 2 cubes (interlocking ones should be taken apart). Can you make 2 even groups? yes, so it is an even number. Display these, then draw pictures to go with each adding labels for the odd and even numbers. i didn't check, but www.superteacherworksheets.com did have some odd even practice pages at one time.