Number lines are great! Once children have become used to counting up and down in single digits and can count up to 10 and back to zero confidently, they can be encouraged to count in steps of two (2, 4, 6, 8, 10). Don’t try this until they are really secure with counting in ones and only go up to 10 to begin with.
Number lines are really useful for this, especially when doing maths at home. Your child can hop along, or draw arrows, to show the path taken whilst progressing in twos along a line. Encourage counting out loud and saying the numbers that are landed on. Don’t forget you can make your own number lines at home, very similar to the old hop-scotch on the driveway or path.