"I wanted to go for something more childlike and down-to-earth," she said.
"I know there are a lot of Bratz fans, but the dolls are so oversexualised.
"I don't think having dolls with tonnes of makeup, short skirts and skimpy T-shirts sends our kids a positive message."
Tulletha said she has been interested in the philosophy of upcycling since she was young, having "always shopped at Sallie Army stores" and making bedroom furniture out of old shipping crates.
She started Earth Kids after reading about Tasmanian artist and Tree Change Dolls creator Sonia Singh, who began repainting fashion dolls she found at secondhand markets.
"I thought, 'I'm crafty, I could do that.'
"I saw a Bratz doll in an op shop in Masterton, and thought, 'it's a sign'."
Tulletha began sourcing Bratz from charity shops and online, and now has "about 60" ready for transformation.
To be reborn as an Earth Kid, the dolls are treated to a "day spa", where they are washed, their faces scrubbed with nailpolish remover, and have new faces drawn with acrylic paints and watercolour pencils.
Their new wardrobes are fashioned from hand-me-downs Tulletha collected from the Wairarapa Resource Centre, hand-stitched with guidance from a T-shirt upcycling tutorial on YouTube.
She also makes their shoes from scratch, using moulding putty and hot glue.
"It's a big commitment, as each doll takes about eight to 10 hours.
"But it's fun -- you feel like a kid again."
Through her upcycled dolls, Tulletha hopes to inspire a new generation to embrace the "make do and mend" philosophy.
"We need to instill that in young people -- that we can make something with the resources we have, rather than just running out and buying it.
"We live in an age where we can get everything straight away, and all those old school recycling mentalities are disappearing."
Tulletha plans to make a "ranger" series of dolls to sell at Pukaha, and auction for Save the Kiwi Awareness Week next month.
More information on Earth Kids NZ is available at: www.facebook.com/EarthKidsNz.