Hi Annamaria,
I'm not a children's writer, but this is definitely a topic that is of interest almost regardless of what style of writing you do. I've heard people say that they make themselves write an hour per day, 2 hours per week minimum.
For others, they say don't force it - the time will come when the inspiration comes.
I'm leaning toward making the time to write just like you do everything else because writing time can get taken over by so many other projects. But when I'm not inspiried, I can't write. So that would be 30 minutes of starting at the computer screen...lol...
Great article!