As I said, this is not about YOU specifically. The same way I would not be a good source if people wanted to know about Czech collocations or idioms. I could only tell them what I know, what I'm used to, not what is generally acceptable or widely used in Czech.

And I think you DID make it absolutely clear that YOU would not say it. So I wasn't criticizing you in ANY WAY. I was just reacting to Cortes' comment – he found it strange that you as a native speaker would never say that. My point was – it's completely natural, nothing strange or surprising about it. Different people know and use different collocations and different idiomatic phrases.

Oh I know – I didn't take it as criticism at all! I was just thinking to myself that sometimes I make absolute statements like “no one would say that” and I was reminding myself that I need to make sure I make it clear that I myself would or would not say it. 

Results of my informal survey – except for the Scottish guy, not one person would use “pet” for people. This included both AmE and BrE speakers. Just out of curiosity, I checked my huge Fronek Czech>English translation dictionary and he says for LASKAT: caress, cuddle, fondle; LASKAT SE: cuddle, hov. snog, pet.

The “pet” in this case is about touching in a sexual way…

A curious thing – I would NEVER EVER EVER say the word LASKAT in Czech. I've never used it and I've never heard anyone else use it in conversation either. 

Maybe it's because the the original question was in Slovak not Czech…

But I definitely agree that TO PET A CHILD sounds weird. I did a little research of my own, spent a few minutes with Google and I found a few hits, especially in Google Books. Maybe it's just a thing you find in books.

(I tried googling “petted the child, petted her daughter” and a few other phrases)

“Pet a child” could very well be older usage…

But even our good friend Google Translate translates it from Slovak as “caress, fondle” – both of which in current usage have sexual overtones, but they didn't always.

What strikes me, though, is that all the dictionaries I mentioned (Oxford, Cambridge, Longman, Macmillan AND Merriam Webster) still mention the collocation. And they are all based on contemporary corpora, or so they say. Why would all five include a collocation that is old-fashioned or literary?

It is very strange. My small sample included mainly Americans, but several Brits as well – from England, Scotland and Wales – and only the Scot said he would say it.

Isn't there a website that shows the frequency of collocations? I think I have the link somewhere – I'll see if I can find it. Google is useless in this case 

Actually not entirely – if you google “petted the child” you get hits, but many duplicates, and clearly not modern literature.

I tried the American corpus: http://corpus.byu.edu/coca/

In the search bar I wrote pet a [nn*], which searches all phrases with pet (as a verb) and nouns.

The most frequent phrase (only 4 hits though) is pet a dog and there is no “pet a child” phrase found. Seems like the verb pet is mostly used with animals.

If it makes you happy – I learnt this word from my Canadian relatives a few years ago and the context was clearly about people, “pet your boyfriend/gir­lfriend sitting next to you” etc. And only much later did I discover the word “stroke”.

Would you use it with anyone but a boy/girlfriend?

To be honest, I have never thought about it much. But the examples they gave me then did not seem too intimate.

I think in the final analysis, technically it's usable, but it's not common usage. To the OP – I'd stick with petting animals, not people, just to be safe and to be sure that you're not misinterpreted