Two of his children were "merely paddling in the water" when "a wave lapped in well under knee height".
"Any currents were way out in the channel where the kite surfers were playing," Tuson said.
"Then after a minute, Logan appeared to stumble - as described by his sister - and got sucked into what must have been a rip that appeared to form as the tide went out.
"My walk to join them soon turned into a sprint as I saw Logan struggling and getting pulled away from his sister.
"I entered the water, and ensured she got out as she struggled in what had now become a very strong current."
As Tuson swam toward where Logan had been seen, the little boy "disappeared from sight".
"The water was eerily murky and I could not see under the water," he said.
"I swam out a bit further from where he disappeared and quickly was in water over my head and being sucked out.
"In vain I looked again under water, reaching out and then resurfacing, screaming out to my boy.
"There were other people on the beach but apart from one other man no one came to assist."
Tuson said he then had to abandon his own rescue attempts as he was struggling in the surf.
"[I] swam back to shore and then ran along the beach panic stricken looking for a way back into the water hoping that he would be washed ashore".
"However the current must have taken him out to the bar, where he was eventually recovered from by the CoastGuard an hour later.
"It is a memory that will haunt me forever."
A spokeswoman for the Tuson family said: "People need to be aware that strong rips can be in shallow water too and that rips can form within seconds and disappear in seconds.
"The whole thing is just a complete and utter tragic event that has left behind an enormous trail of heartache and grief."
Logan's funeral was held at Hamilton Park Cemetery on January 15, and among family and friends were representatives from Hamilton's Te Totara Primary, the school he attended.
Te Totara's acting principal Anne Fraser said the school was working with staff from the Ministry of Education trauma team, around how to acknowledge the loss of Logan when the school term begins in a week's time.
"We are just working really closely with the family. It is their tragedy first and foremost and we want to be very much walking with them in that journey."
In a tribute on the school's website, which the Tuson family had looked over before it was posted, the board of trustees said: "We are all shocked and devastated by his passing in such tragic circumstances."
"As school staff we pour all our energies into educating and caring for the children and to prepare them for their future, never to expect that it would be cut short at such a young age.
"Logan's teachers over the past three years have described him as a 'beautiful happy boy, a caring classmate and a wonderful friend'.
"He had become more confident in his education journey and was excited about sharing his ideas with others. He had a wonderful imagination and should have felt very proud of his achievements."
There have been 12 water related deaths in New Zealand so far in 2019.
