Skip counting is the most common way to introduce children this young to the concept of multiplication (e.g. 2,4,6,8 or 5,10,15,20). The website below gives you lots of ideas, including manipulatives (objects) the child can use, songs, actions, etc. Toward the bottom of the page, (Skip Counting Leads to Understanding Multiplication) it shows how to extend skip counting into multiplication by grouping objects on pieces of colored paper and counting the number of groups - one of the clearest ways to illustrate multiplication:

http://www.squidoo.com/counting
For fast learners, I have also used rectangle multiplication from the National Library of Virtual Manipulatives. It shows the concept in grid form. You can translate that to physical manipulatives by having the child duplicate the grid with objects, then having him or her wrap string or yarn around groups (e.g. five groups of five = 25):

http://nlvm.usu.edu/en/nav/frames_asid_192_g_1_t_1.html?from=category_g_1_t_1.html
It's good to introduce a child to the grid format because by grade 3, standardized math test questions often require interpeting shaded boxes in a grid.