UPDATE: I've officially received and accepted another teaching position after charter school founder told me “you chose to have kids” and warned my contract renewal could be in jeopardy if I missed too many days next year

LINK to my original thread for more context/backstory.

A while back, I posted here about an absolutely surreal contract renewal process at the small charter school where I taught the past two years.

For those who didn’t see the original post: I’m a father of three young kids, and this year I used around 12 sick/personal days total out of the 15 days allotted to me by contract. Most of those absences were related to sick children, medical appointments, and a personal illness that I’ve honestly never dealt with before in my 10-year teaching career.

During two separate renewal meetings, the founder/president of the school told me the following:

• “You chose to have kids.”
• “You can’t treat this like just a job and push it to the side to stay home with your kids.”
• “Your wife and you are both taking advantage of the system by using all of your allotted sick and personal days.”
• "You and your wife make six figures combined. That should be enough to afford a nanny/childcare professional to babysit your kids when sick."
• “Your name and situation came up at a school board meeting and one board member advised not renewing your contract.”
• “Finding another social studies teacher won’t be hard.”

I was also repeatedly warned that if I missed “too many” days again next year, my contract renewal could become a problem. The founder/president of the charter school wanted me to promise I'd have a plan in place next year to miss less days.

At the time, I still signed my renewal contract with the charter school because I had not yet secured another position, and with a wife, mortgage, and three children, I couldn’t risk walking away from stable employment without another job lined up first.

After applying for jobs, I almost immediately got called in for interviews (four total in the past month). And today, after a callback interview for one of the positions, I was officially offered and accepted a job teaching middle school social studies!

I’ll be returning to the same large public school district where I spent the first seven years of my teaching career before leaving for this charter school. The new position also comes with roughly a $6,000 salary increase, which is obviously huge for my family.

But honestly, the biggest relief is simply escaping the stress of working under someone who made me feel like caring for my own children was somehow evidence of professional irresponsibility.

Now I’m looking for advice from other teachers:

1. How honest should I be in my resignation letter? Should I keep it extremely brief and professional, or should I mention how inappropriate and unprofessional I found those comments and meetings?
2. Should I email my coworkers to let them know I’m leaving? We’re already on summer break, so email is really the only option. I genuinely like my coworkers and don’t want to just disappear without saying anything. But I also don’t know whether I should be honest about WHY I’m leaving or keep it vague/professional?
3. For those who have left toxic school environments before: do you regret speaking up, or regret staying too quiet?

At this point, I feel relieved. After my first (of two) meetings with the founder/president of the charter school, I refused to work for someone that treats basic parenting responsibilities like a failure and/or lack of professional commitment. Now, I just need to figure out the best way to break the news to my coworkers and boss.