Prime Minister Jacinda Ardern hits the right note with piano cake for Neve's second birthday

Prime Minister Jacinda Ardern has celebrated her child's second birthday with a structurally unsound piano cake.

Neve Te Aroha Ardern Gayford entered the world on June 21, 2018, making mum just the second world leader in modern times to give birth while in office. 

In a post to her official Instagram account, Ardern showed off the toddler's cake - which she acknowledged didn't quite look right.

"Cake making lesson number two - don't focus on making the cake look in proportion with little to no attention on structural integrity," she said.

"There is a jar of lentils propping this thing up. Happy Birthday Neve! Thanks for ignoring all of the imperfections in life and just being a joy."

Musicians will note the keys appear to be arranged incorrectly - but it's unlikely Neve will care. 

"It's made with love and that's all that matters," one of the Prime Minister's followers commented.

It's the second year in a row Ardern has baked a cake of dubious quality. Last year she made one of a bunny rabbit, saying it was not an enjoyable experience - but the fact it was covered in coconut hid any imperfections. 

"Who knew that kids cake recipes had so many swear words in them?" her partner, TV host Clarke Gayford, tweeted at the time.

This year he claims mum didn't swear at all.

"Can confirm 100 percent less swear words went into this year's cake," he wrote on Instagram. "Well done mum."

"Well done Mum... the cake looks good," one follower told Gayford.

"Looks good, I guess it makes you a key worker," another commented.

Both cakes were based on recipes Ardern found in a cookbook published by the Australian Women's Weekly.