I mean yeah, sure spoil them as grandmas do, but if it's making them sick and giving you a big mess of vomit and diarrhea to clean up every time then you're definitely doing the right thing! there's nothing wrong with setting boundries for your children and you know what's best for them. I had to tell people to stop giving my kids chocolate for Easter because it would give them insane diarrhea (they're fine now) luckily everyone understood.

Babysitting vs making them sick are two different things! Stand your ground until she can be a reasonable adult.

GOOD. Spoiling kids means doing things they enjoy, not making them physically ill. Making them some new delicious real food would be spoiling them, not getting them horribly sick. You are a Good Parent, OP. (And if your kids like sweet things...might I recommend some new fruits? Dragonfruit or mango sounds like a good treat for kiddos, and fruit in exchange for cleaning up toys works wonders.)