If genes were involved we would expect the prevalence to be different, but there is no way that not a single South American child has the right genes for sugar rush.
Is sugar rush a culture-bound syndrome?
Curiously, my friend's partner's Argentinian, so... .
If the dominant component really is physicalist/biological then things that actually contain sugar but don't look like they contain sugar will cause sugar rushes. For example fruit juice, ketchup, pizza.
If it's cultural/psychological then only things that are "sugar-coded" will produce the effect. Like candy, syrup, ice cream, soft drinks.
If you feel like doing some mad science, see if you can give your kids a rush using sugar-free coke or something like that.
Also, I'm 'one of those' and avoid sugar-free alternatives.
For sure though, I can't say I've much noticed it in the likes of fruit smoothies and such, nor when she has a lollypop or some other sugar-laden thing that takes time to consume.