Mrs Leslie said all their children had grown up and gone to school in New Zealand.
From India, Mr Santhosh Mathew, his wife Bindu Patterukudiyil Kuruvila, and daughters Anova Santhosh and Alona Santhosh wore their national costume to the ceremony.
"Thank you for having our family here. We thank God and are really proud to become citizens of New Zealand, our wish has finally come true," Anova said.
Returning to mayoral duties after the death of her husband John, mayor Steve Chadwick led the ceremony.
"It's a lovely ceremony. You can feel amongst us today for some it's a huge deal because they have to renounce their country of origin and you can never take out of your heart your mother country... New Zealand is seen as a safe country with good values."
The five members of the Foliaki family, from Tonga, were thrilled to become Kiwis.
Meliame Foliaki said they were "very proud to become tangata whenua".
She laughed as she said she had been told by her husband to keep her record clear so they didn't get sent home.
On behalf of the Kataria family from India, daughter Ayushi Nareshkumar Kataria said they arrived in New Zealand 10 years ago. "Thank you for having us today."
South Africans Clinton Marcelino Petersen and Alana Petersen had been in New Zealand for 17 years.
Mrs Petersen said they had finally decided to become citizens.
"We're really proud to live in Rotorua and call New Zealand our home."
It was a tough decision for Sini George and her family to chose to become New Zealanders.
Alongside her four children, Mrs George told those gathered it hadn't been easy to give up her Indian citizenship.
"I promise to New Zealand I have four beautiful citizens for you. I will bring them up as faithful citizens in this country."
The ceremony included items from Kawaha Point Primary School and a welcome video message from Governor-General Dame Patsy Reddy and Minister of Internal Affairs Peter Dunne.
New citizens received a book titled Choice and a seedling.
Two Australians, five Tongans, 14 Indians, two South Africans, one Irish, one British and two Fijians became New Zealand citizens.