TBH it sounds like the CSR and her super don't know what they're talking about. If it is set up as they say, then I think you're right, and it's not entirely above board. Which is why I think they don't understand the "why" of the pricing.
Realistically speaking they're probably pricing this like a standard buffet might - one price for Age X and under, another price for everyone else, since (in theory) teens and adults eat more than kids (I say in theory because my niece is an eating machine). The fact that sparkling wine is available to those of drinking age (in the US) is meant to be a bonus, and if we're being honest, sucks for anyone aged 13-20.