I saw a man park in one last year with his son. His son was about 17 or 18. The dad went in and shopped without him whilst the son played on his phone and looked embarassed at my glaring at his dad!
I did calm down enough to realise it wasn't his fault his dad had done this! The spaces in this particular supermarket car park specify children under 5.
Wish I had got them to say over the tannoy that owner of his car had left a 'child' alone in the car!
If I see no spaces in the parent and child bit or I feel tired and know seeing someone use one who shouldn't will wind me up I park in an end of row space with space to get ds out.
As for parking in them when you are pregnant go for it! I have an almost 2 year old and I can def walk further than I could at 42 weeks pregnant! Seriously more preg women should use them. You are parent and child and as one unit physically it is hard! At least I can put my bundle of joy and madness in a trolley, you can't take the bump off and feed it free bread samples haha