Von Dadelszen and King also competed in last year's national final in Invercargill.
Abby Strang, 11, Stuart Addis, 12, and Chalkie Williams, 10, from Tikokino School won the fiercely-contested AgriKidsNZ contest.
That regional final saw 144 students, working in teams of three, take on a series of fun modules.
They included fitting tyres to a Honda quad bike, assembling a Hansen water system, a WorkSafe hazards challenge and correctly identifying different breeds of sheep and cattle.
Ben Gray (left), Sam Lawson and Rose Beamish from Ongaonga School came second in the AgriKidsNZ contest. Photo / Supplied
Ben Gray, Sam Lawson and Rose Beamish, from Ongaonga School, placed second.
Harrison Brown, Sheldon Brown and Harry Bourke from Pahiatua School were third.
All three teams have qualified for the AgriKidsNZ Grand Final in Hawke's Bay.
Both national finals will take place alongside the prestigious FMG Young Farmer of the Year Grand Final in July.
The FMG Junior Young Farmer of the Year competition was formerly known as TeenAg.
Both events are a key part of the work being done by NZ Young Farmers to attract students into the agri-food sector.
East Coast regional final results:
FMG Junior Young Farmer of the Year
1st Finn Beamish and Matthew Halford. Napier Boys' High School 2nd Guy von Dadelszen and Macabe King. Napier Boys' High School 3rd Isabel Greville and Kaylee Hutchinson. Woodford House
AgriKidsNZ
1st Abby Strang, Stuart Addis, and Chalkie Williams. Tikokino School 2nd Ben Gray, Sam Lawson and Rose Beamish. Ongaonga School 3rd Harrison Brown, Sheldon Brown and Harry Bourke. Pahiatua School