The children are non-identical twins, biologically the son and daughter of Mr Fitzgerald and from eggs that came from the same donor, a Thai woman.
The Fitzgeralds married almost 10 years ago and quickly realised they needed help to conceive a baby.
Mrs Fitzgerald went through three cycles of in-vitro fertilisation (IVF) and one round of treatment with donated eggs, all without success.
The couple explored adoption and Mrs Fitzgerald had two rounds of donor egg treatment in Thailand, but that, too, failed.
By this time, Mrs Fitzgerald, a technical manager in the meat processing industry, was becoming desperate about her unexplained infertility.
"I just couldn't not be a mum," she said yesterday, weeping as she recalled the pain and depression.
"I almost felt like a bit of a failure not being able to have children.
"To be honest, I didn't care where the kids came from, I just wanted to be a mum."
An Australian couple they met through their Thai trip put them in touch with Thai fertility specialist Dr Wiwat Quangkananurug, which led to them making surrogacy arrangements with his clinic.
Mr Fitzgerald, a private investigator, went to Bangkok, where the embryos were created and some were frozen. The surrogate - who, like the donor, was chosen by the couple - had an embryo transferred into her uterus.
About five weeks before Johnny was due, the Fitzgeralds received a call from Thailand to say the surrogate was giving birth.
They rushed to get there, arriving a day after the delivery.
Legal processes, including DNA testing to prove paternity and other paperwork, kept them in Thailand for another five weeks, before Johnny was granted a New Zealand visitor's visa, enabling the Fitzgeralds to return home with him and complete the adoption process.
Mrs Fitzgerald said they contacted Child, Youth and Family before Johnny's birth and officials didn't seem to know how to deal with the matter.
The process involved three government agencies and she said it was only when she appealed to her local MP, Simon Bridges, that progress was made.
She said it was crucial to be allowed to have contact with the egg donor and the two surrogates because the couple wanted their children to know where they came from.
They met the surrogates and kept in contact with them and the donor.
The surrogates were aged in their early 30s and mid-20s and had had their own children. Mrs Fitzgerald did not know how much they were paid.
The clinic costs were around $34,000 for one IVF cycle and two surrogacies, but legal fees, accommodation and travel pushed the total to around $60,000 for each child.
Money well spent? "Completely. It's the best thing in the world.
"I don't think I would feel anydifferently about these kids if I'dhad them myself. I'm completely besotted."
What is surrogacy?
*Surrogacy occurs when a woman has a pregnancy on someone else's behalf and hands the baby over when it is born.
*It takes various forms, including natural conception by intercourse with the commissioning man, artificial insemination with his sperm, or transfer into her uterus of embryos from sperm and egg from the commissioning couple or from donors.
*Altruistic surrogacy, where no money changes hands, is permitted in New Zealand under strict conditions, including that one of the intending parents must be a genetic parent of the child.
*Commercial surrogacy is banned in New Zealand but is legal in some other countries.
Overseas surrogacies create 20 Kiwi kids
Nearly 20 children in New Zealand have been born overseas as the result of deals in which a woman is paid to carry the baby in her uterus as a surrogate mother.
The Fitzgeralds understand they were the second New Zealand couple to enter an international commercial surrogacy arrangement, for their first child, Johnny, now aged 2.
Immigration NZ said that since August 2010, visitor visas have been issued to 18 children who were born as the result of international surrogacy agreements.
A visitor visa is one step on the complex path of adopting such a child and obtaining a New Zealand birth certificate and passport.
The Fitzgeralds' lawyer, Margaret Casey, said the number of couples seeking international commercial surrogacy was growing.
"[Immigration] is saying about 18. I think, given the inquiries that I'm getting, it will be double that by next year," she said.
Commercial surrogacy is banned in New Zealand, but is permitted in some countries, notably India, Thailand and the United States.
The head of Surrogacy Australia, Sam Everingham, told a fertility conference in Auckland this week that more than 350 infants were born to Australian parents last year through international commercial surrogacy.
