Unfortunately there's only so much that can be done even with high-quality and comprehensive language education that doesn't take up a large portion of school hours - overcoming the hurdle of getting enough exposure to the language without having any interaction with it outside of a few hours per week can never really let you get past A1/A2, especially in output. Lots of parents will also just balk at their child being bilingual for reasons of either racism or a desire for control (or both!) so that avenue is also pretty hopeless for a lot of people. Honestly, outside of having proper bilingual education and schooling, if there was a way to introduce tools like Anki to kindergarteners in a way which wasn't overbearing or shitting on their natural curiosity it probably wouldn't work half-badly lol