Listen to @Flowertop845 who has actually done the job, vs some advice that is either out of date or very niche (guarantee that hardly any HR admins know Excel macros), or very bitter.
I'm not in HR but often work with them - like any job you get good and bad, and it is definitely fair to say that you do have to be conscious that if push comes to shove you're there for the business over the employees. However, good businesses know that having the right people is critical to doing well, so it's not all the type of supervisor stuff that public sector people describe here. I've worked with HR teams who have dealt with and fired bullying managers, hired in great new people, ensured that employees have access to funds for training and development, or more recently worked late for days to rework benefits so that US employees had coverage for terminations post the Roe v Wade overturning. Yes, more senior HR people (not admin or training people) do also have to deal with performance issues, tribunal cases and redundancies, but being able to handle these well and with respect for the individuals going through this can make a big difference for those involved.
Because there are (frankly) quite a lot of people in HR with limited idea of what the business is doing, if you do work moderately hard (less than you are now as a teacher!) and/or are more ambitious, you do also have a good chance of promotion, including part time. Senior HR leaders are incredibly important to a business and work closely with leaders.
As some of the replies show, you'll also have a v different time if you're working in a fast growing tech company or in an NHS post or a call centre.
However, I think it's a far better path than your other suggestions of office manager or general admin, in terms of long term potential. You can get professional qualifications, it's part time friendly, and there are many pathways, from talent/recruitment to benefits management, to learning & development. And dealing with small children will have given you the skills to take on even CEOs (maybe especially CEOs)... good luck!