Sometimes what you're advertising isn't what you meant to say

I've just come home from brunch with friends down the posh end of town, and as I crossed the road to return to the car I became mesmerised by a large banner slung overhead across King William Road. It was an ad for Pulteney Grammar School, one of Adelaide's pricey private schools, showing a picture of a little girl with plaits, bent studiously over an exercise book.

Above the photo, in giant letters wholly innocent of punctuation, appeared the following exhortation:

SEE YOUR CHILD DISCOVER WHO THEY REALLY ARE

(Thinks: 'Hello darling, how was your day?'
'Excellent! I saw Ermintrude discover who they really are!'
'Who who really are?'
'Ermintrude.'
'Um, what?'
Etc.)

Now, I don't have any kids, and if I did they'd probably be beyond school by now, but if I had and they weren't and I was looking to educate them, any school that advertised itself using the so-called 'singular they' would get crossed off my list sharpish.