Did your child confuse the number of groups with the number in each group?  If so, please practise grouping using household objects.  Your child can use plates for the groups and other objects from your home (such as sweets, spoons or building bricks).  For example, you could give them 10 spoons.  Can we make equal groups of 2?  How many groups have we made?  Encourage them to describe what they have made.  In this case, it would be 5 groups of 2.