"We keep him well and healthy. He spends maximum time in Conductive Education, his special needs pre-school, and they work really hard to drive his progress," Mr Burton said.
"His last vision test was reasonably positive. He seemed to follow a light a little bit. We've also noticed that he can track sounds when he wants to. What has been really pleasing, he's done quite a lot more smiling."
But because of his brain damage, it remains to be seen how much William can see and hear.
"I think maybe the brain is kicking on and developing slowly and responding to external stimuli, to a very limited extent," Mr Burton said.
William goes to Conductive Education for 2 days a week and also into respite care.
The biggest news for the Burton family over the past six months was Wellington Hospital reversing its decision not to offer William life support if he needed it. That reversal was made shortly after the family told their story last year.
"As soon as it went public the reaction from everybody was great and a lot of pressure was brought to bear on the hospital and their appalling decision. They backed down," Mr Burton said. "If he's in danger again, he will have the life-support option."
This year his parents hope to start him on a riding with the disabled programme, but he may also need an operation on his left hip.
They'd also like to build his strength, particularly in his neck muscles.
"That's going to be a long process," Mr Burton said. NZME