The memory of your kid is sharper and stronger than you perceive. It is just that he has recently started memorizing, it becomes a bit difficult for him to remember things. Begin by teaching him the home address and phone number.
What you need to know:
This should be the first thing that you need to help your kid memorize for his own safety. Making him learn his home address and phone number is also an early sign of analyzing his memory skills. Some kids learn things quickly, while some take time to memorize. Give special attention to his diet and start including more of memory boosting foods in his daily meals.