Kvass is low in alcohol, but it will still knock your socks off. The Russian beer-like beverage is centuries old and, as a base, made from fermented bread. From there, any number of things can be added, including raisins, honey, mint, birch sap, fruit and more. It's basically the kitchen sink approach to fermentation. What comes out is kvass beer, a sour drink that's right at home in the Russian flavor profile.
The living drink (think kombucha) has recently started to make a comeback in the craft community. As for its history, since fermentation can kill bad bacteria, it was often safer than drinking questionable water, even with an ABV of 0.5-2.5%. So, sure, the flavor might be strange, but if kids have been drinking it for centuries, surely you can handle it.