Will you please provide some additional context here as to why and how Duolingo is poor at language acquisition? What software is better at language acquisition?

Are there other apps that are more effective?

Yeah I get that. I don't think my son is ready for something effortful like LingQ. So, even if Duolingo is only a tenth as effective per unit of time spent, it's better than nothing.

With Voiczy, we recommend limiting sessions to 15-20 minutes per day. We plan to add more games in the future to make learning even more enjoyable. Given that children (and even adults) have short attention spans these days, consistent daily practice can make a significant difference over time. After a month or two, you’ll likely notice great progress!

We’ve seen excellent improvement with our son using Voiczy daily. Of course, we know we’re not perfect. We're just a small parent-run company. It’s just me, my partner, and our son, who happens to be our main tester! :)