There are at least 7 parts to counting a group of objects:
–  memorizing the names of the numbers
–  saying them in a certain order
–  connecting each number-word to an object to be counted
–  recognizing the repeated 1 – 9 pattern of the numbers
–  understanding that the final number said is the total quantity in the group
–  knowing that the order in which we count the objects does not affect the total
–  believing that the number of objects in a group stays the same even after they are rearranged

Try This

Start by having your child count a small amount that you are pretty sure he can handle with confidence. Then gradually increase the quantity until you reach a number at which he has difficulty. Have him count that many objects until he becomes comfortable with that greater amount.