I worked as an early interventionist for many years. You should make learning his numbers as fun as possible and offer him many experiences to do it. How about printing off simple number pages off the internet. You could colour them, and cover them with clear shelving paper to protect them. Post them on your fridge, but them in his bedroom. Make it a routine to practice them every day. First start out with him identifying them. Start with just a few numbers, and tell him what they are. Ask him to point to the numbers to get started. Once he can correctly identify the few numbers by pointing to them, increase by one or two numbers. Take it slow and praise him for his efforts.
They are great number activities on the internet, and in stores. Consistency will really help him. Do number crafts at home. Cut our simple numbers out of construction paper and have him decorate them. Again start with just a few numbers.
Always do what you want, and say what you feel, because those who mind don't matter, and those who matter, don't mind