The authors, Glenn and Janet Doman, remind parents that quick is best and not to ask the child to repeat the numbers.
Now the fun begins. Simply hold up the 'one card' just beyond his reach and say to him clearly and enthusiastically, "This is one." Show it to him very briefly, no longer than it takes to say it. One second or less. Give your child no more description. There is no need to elaborate.
Hope this helps