Quite apart from the immersive experience of shopping, (how on earth do your grandchildren get properly fitted with new shoes, maydonoz?), children are missing out on understanding of money and how it works. They never see or handle it! They never see it given in exchange for goods!
Anyone who has tried to teach young children about money will know how difficult it is. As for handing it over and expecting to get change....that's a non starter. You could give them a £20 note for an ice cream and they'd come skipping back from the van with their ice cream i.e. no change! I've set up so many classroom shops and observed children handling 'money'. Understanding of money ought to begin at home. (Not to mention toilet training, hand washing, shoelace tying, speaking in sentences etc.) No wonder so many younger people are in debt when there's no connection between the plastic cards and actually having money. I never used to understand the saying, 'You can't have your cake and eat it!' but I would've understood, 'You can't spend your money and still have it!' Of course, ever increasing credit limits mean you can...up to a point when the bailiffs come knocking on your door!
Yes, I'm a retired Key Stage 1 teacher. Did you guess? ??