Glycerol and ethylene glycol (antifreeze) are very different in toxicity and effect. The reason for the caution for children under 4 in your article is because of its use as a laxative. It's not at all the same as vehicle antifreeze (which is toxic in moderate quantities, mostly dangerous because it's also sweet so kids and animals will drink a lot of it.) Propylene glycol is a secret third thing (also antifreeze, but relatively non-toxic - less so than alcohol - and is used in some food manufacturing but for different applications.)

Putting it in slushies sounds like a terf island thing? In burgerland we typically use HFCS because it's cheap as hell. The ICEEs listed here specifically use HFCS and carbonation for lowering the freezing temperature.