"Au pairs are s**t," announces a friend. "Sam has one who doesn't speak a word of English." And there it is. The universal conversation on au pairs. As bad as birth, everyone has a horror story. Au pairs nicking valuables, leaving kids at school gates, weeping hysterically and running off in the middle of the night.

Meanwhile au pairs have their own Facebook pages dedicated to slagging off their host families detailing our appalling behaviour. Dreadful food, filthy houses, locked fridges, vile Von Trappish children (pre Maria), mothers hitting the fathers and worse.

Au Pair
Good au pairs are worth investing inistock

The Guardian is also on it. Outraged that middle-class families are paying people £3 an hour to look after their children. Which does sound appalling. Until you consider how many people might quite like £100-plus a week of totally disposable income after every bill (rent, food, phone, travel, Wi-Fi) has been paid. While they are young, leaning English and having a whole new life experience.

So I'm challenging the normal chat and going out in favour of au pairs.

Firstly, if you have a spare room it makes financial sense. The system is outside of the tax system because it is based on the idea of a cultural exchange: your au pair must be from another country and learning English.

They live in your house and eat most meals with you. They are expected to work reasonable hours – the government cites 30 hours a week – in exchange for pocket money. Which might be anything from £75 to £150-plus a week. If you have a spare room and you rent it and use the money to pay a nanny, you will potentially pay tax on both. An au pair could be a good option.

We've had a few. Half utter gems. Half who weren't a great fit.

The success factor? At the risk of sounding like your head of HR, if you hire someone that someone else's Italian mate said would be "perfect" then a stranger will appear on your doorstep with low expectations and, very probably, more desire to party than face paint.

Your kids will hate them, the house will lay in ruins and you will be so scared of hiring someone worse you'll be terribly British and put up with it for months. There is a better way. Unfortunately it is time-consuming and boring.

Spoilt child
Communication is a two-way streetistock

Start with advertising where the best candidates are: we like AuPairWorld. Others use agencies but reviews are very mixed. Then make a proper effort to make the job appealing. Pictures of their room, information about the area, pictures of your kids, good pay.

Be honest and specific about what you need and expect but hold back on bullying lists of chores and petty house rules. You want the best applicants not the most desperate.

And then wait. Last time we got 190 applications in three days, including qualified primary school teachers and nursery carers. We live in London, which helps, and our kids look like angels when you can't hear them fighting over which one is Elsa from Frozen.

When you have a decent list, narrow down your search – older applicants, who have worked before, may be more mature, childcare experience is a must (don't buy any nonsense about their cousins), willingness to help out at home. Interview on Skype a good few (10 or more if you can): keep track in a spreadsheet, meet any already in the UK. Speak to them twice or three times as you get closer to a decision. Take proper references. Then draw a deep breath and choose.

Mary Poppins

Face-painting
Having fun with a bit of face paintingGetty

It may just be that Mary Poppins will appear on your doorstep, with or without an umbrella. She (or possibly he) will know how many you had to choose between.

They will have invested time, effort and risk in you: just as you have in them. Both sides will be determined to make it work. If you are very careful and a bit lucky, they'll get energy from being with your kids, be delighted to experience a new country and your whole household will be happy to see them.

If not, strap them on and bail fast. There are loads of brilliant people out there and you owe it to your kids and yourself to find one.

Treat them like treasure

When you do, treat them like the treasure they are. Any time you have doubts about level of holiday pay or having their friend over, there is a foolproof way to get the right answer. Think forward to when your darling child is their age and living in Moscow or Beijing or Rome with a family. Ask yourself how you would want them to be treated. You know the right answer.

Christine Armstrong is a contributing editor of Management Today, author of Power Mums (interviews with high-profile mothers) and founder of www.villas4kids.com. She can be found on Twitter at @hannisarmstrong.