Pierre, thanks for sharing this information. It's nice to see a post on HN that does not talk about making hundreds of thousands of dollars after throwing something together over a weekend. The vast majority of successful business ventures --of any kind-- take time. Generally years.

It's also nice to see an example of a lifestyle business rather than a mega-million-dollar exit startup that so often dominates the headlines in these communities. Quite a few developers would be more than happy to earn a third of what you have earned on a regular basis. And that would be considered to be an absolute success.

I too am delving into the educational-app-for-kids market inspired by my own kids. I'd enjoy the opportunity to get some feedback from you if you are open to it. My email address is in my profile.