In this scenario it may be best to presume that you have not given Hepatitis A vaccine and give two fresh doses as per the schedule. You can find out whether the child has become immune or not after giving one dose as indirect evidence that you gave the dose first time. However, the cost of this test may be as much as the cost of giving one extra immunization, which would be entirely safe and may even enhance immunity if the child is sub-immune with earlier two doses