I can see why a parent might HAVE to leave a child- if on their own with them anyway; on several occasions some idiot has parked so close to both sides of the car that I could not get rear doors open and car seat in. Luckily drivers have usually returned swiftly but that's been luck.
I use P&T spaces with my boys aged 3, 8, 10 and 12- very rarely but on occasion. They are all disabled (well, ds4 and ds2 in assessment but definite SN somewhere) and yet not enough for a disability parking space. Mostly I steer clear of leaving home without an extra adult anyway but if I have to then so be it.