It might be worth speaking to your health visitor about a condition called glue ear, fairly common in children particually after a cold, otherwise make sure you actually have your childs attention when speaking to him, often children just tune out to what we are saying because there interest is elsewhere at the time, a good way of making sure he has taken in what you say to him is to ask him to repeat what you said, then at least you know he has heard you and understands what yuou are asking him to do.