You’re making a really good point…
Unfortunately, lot of (if not all) primary franciscan source literature has that kind of stuff in it… back then… I think that is just very much how they knew to regulate themselves… and, yes, some of it can get to be a bit much to the modern ear…
In a way, while I believe you couldn’t find too many saints tougher and yet gentler than St Francis of Assisi, it’s probably good the kids know at least a little bit about the way things used to be… while still clearly defining the way things are today, what’s appropriate, and how they should protect themselves… I’d even make that recommendation
in general - because the Bible itself wasn’t written for children (says Fr Mitch Pacwa), and its hard even explaining something like the crucifixion to kids…
Here’s an idea, however…
You might want to consider a secondary, i.e more recent derivative/interpretive work attuned to contemporary sensibilities and issues (by that I mean written in a modern vernacular and leaving out some of the more severe moments in our churches history)… I’m not versed in secondary source literature, (I’m primarily schooled in and thus familiar with the Classics), but there’s a few videos I know of which you could try… a
video is something you all could enjoy together as a family, and then you could be right there to watch with them, and even answer any questions… also, my experience with buying books for people is - unless you know someone really wants to read a book, you run a great risk of wasting your money…
Anyway, here’s a video I’d recommend…
https://www.monasterygreetings.com/product/The-Birth-of-the-Franciscans-DVD/CD-DVD-DVDs
It’s a three part series that portrays a bit about how the order was founded, highlights a few of the more notable early friars (including the st clare), and describes how they lived as mendicants in a very gentle and appropriate way…