Have children practise to estimate quantities of objects... to make a calculated guess using vocabulary: more, less and same.
Practise writing numbers 1 to 20.
If children are experiencing reversals simply have them flip it over... this will sort itself out! :O)
Looking for patterns on a 100's chart
Count to 100
Counting back from 10
Counting down from 20
Skip counting forward and back by 10 to and from 100