We used these (Cuisenaire Rods Introductory Set) my son was in first grade. Later, I got rid of them in a frantic effort to clean out clutter in my house. A few days later my son was looking for them and became quite disturbed that his math rods had been given away! Apparently they made a great impression on him, and he really dislikes the plastic rods I replaced them with. Maybe your kids will like cuisenaire rods as much as my son does. Timberdoodle’s are wooden and that makes a big difference.
Note from Timberdoodle: Our rod sets are actually a very high-quality plastic, just so you know!