After getting swept into the harbour channel from a rip along the Raglan coastline, Logan's body was soon recovered by Coastguard, but he was unable to be resuscitated on shore.
The stretch of Wainui Beach Logan drowned at was not patrolled by surf lifesavers.
David Tuson said both Logan's 16-year-old sister Rina, and his father Colin were following closely behind the youngster as he rushed across the foreshore, but the danger escalated "very quickly".
"Rina was the first one who tried to rescue because obviously they're racing trying to get into the sea," he said.
"My son was following not too far behind and he dived in as well and obviously they couldn't get there. [It happened] very, very quickly, it was unfortunate the rip was going out just as they got to the water."
David Tuson described the whole family as "very close" and Logan as a "brilliant little kid".
"He was just one of these kids who loved building Lego toys, he loved wandering around his place at Glen Afton which he described as a farmyard," he said.
"He's a fabulous little grand kid ...full of energy and full of life. That's why he perished, he wanted to get to the water first."
The 74-year-old Paeroa resident, immigrated from Manchester to New Zealand in 1974, along with his 4-year-old son at the time - Colin.
Colin Tuson now lives in Glen Afton and Logan's mother, Rosina, lives nearby in Hamilton.
David Tuson says the parents and family are preparing for Logan's funeral at the Hamilton Park Cemetery this Tuesday.
"They're obviously both devastated," David said.
"Colin's devastated because he was there and he watched his son go out to sea and couldn't save him, and Rosina wasn't there and she had to have the news second hand."
Logan's death was the 10th water-related incident in New Zealand in just under three weeks.