For children working on one less, have a go at telling the difference between one more and one less. More could be represented by pointing up and less could be represented by pointing down. Tell you child that one more always means a bigger number and less always means a smaller number.
For children who are understanding one less work on the subtraction work from Session 2 and 3.
For children who are understanding subtraction, tell your child 2 numbers. Ask which one is more. Then say 2 different numbers, ask which one is less. Repeat with different number. Write 2 down and have a go at doing it through recognising the numbers.
For children who are working on the difference, have a go at the work in the document below. See how far you get, don't worry about completing it. Doing the first page is enough.