I absolutely LOVE Cuisenaire Rods for helping children develop their number sense. I posted about them a while ago with THIS POST about using Cuisenaire Rods to practice math facts and fact families. I've got some kids who need to back up even further and really need to get to know the individual numbers by using these manipulatives.
It's a good idea to give the children a couple of sessions for free explorations with the Cuisenaire Rods. They'll catch on that the smallest cubes are always white, and that the longest ones are orange. Sooner or later, they'll figure out the "staircase". From the staircase, they'll figure out the value of each color, so it's a good idea to start them off by building a staircase from this point on.
I've put together a few exercises with the Cuisenaire Rods to help build number sense, Click HERE or click the image to the right for a freebie on the number 5 (the yellow rod).