Do you know the stories? If so, it might not take you very long to write an adaptation. 80/book does sound high and it might be so for the first one, but once you have the structure, you could whip through these. The process isn't linear.*
What kind of deadlines are you facing? Would you have to drop everything else to work on these adaptations? Do you know how fast you can write? So many things to consider. But I do think it's a great way to be published. And you know kids would be reading these books. And that's the BEST part. Also, you'll learn a lot about writing these kinds of books that are very popular with kids and the knowledge you gain, you can apply to your own pet projects. As you can tell, I'm in favor of taking the leap. I've discovered the net always appears.
*As a short story writer, I used to lament the fact that novels are long and if it takes me a year to really polish a short story, then it would take me 50 yrs to write a novel? Not so. For instance it took me 2 yrs to write and revise a novel and working very part-time on it. I joke about Ten Easter Eggs, how it took 10 yrs to get it published, that it amounted to writing half a couplet each year. But we all know that's not how writing works.