How can I enforce boundaries when it comes to my personal time?

I have worked virtually for 17 years, and I took a long time, and actually stepping down from one of my positions, before I realized how much of my personal and family time was being given to the job.

When I decided the work I was doing was "a job" and not the center focus of my life, setting up the boundaries became much easier for me.

I have made it very clear, by simply being honest and transparent, with my employer, that I will not begin work until 9am and I will finish work at 5pm. Those hours, minus a lunch period, are all theirs, and I dedicate and focus my time to the job. But I sign on amd off at those specific times, and then mentally remove myself from that part of my life. Even if texts, emails, calls from clients come in after hours, I completely ignore them, without reservation.

I have found that there is nothing so pressing that it demands an immediate response. Understandably so, in some fields of work, this is not the case. But in mine, literally everything can wait, and there are many polite ways of presenting this to clients/employers. Honesty in communicating the importance of your own mental health and need for time away each day from the job(s) is essential.

Well I can’t agree more, it has become so challenging to maintain a work-home balance while we are working online.
I am someone who has a full time conventional on site job, then I am also engaged in a couple of online assignments. It was initially quite difficult (it still becomes challenging at times  ) but then I gradually developed a work schedule and I try to stick to it (most of the days ).
My kids are old enough to understand when I need rest. Similarly, I organize my activities in such a way that my kids have my full attention when they need it.
I have set realistic working hours and if I feel over worked, I try to reduce work load for some time. Whenever I feel that stress is taking toll on my health, I try to take a break (few days off with family) and it helps me in rejuvenating and coming back with more energy.
Key factor in managing a balance between work and home is COMMUNICATION. Talk to your kids, explain your work requirements, listen to their expectations and schedule your work accordingly.
Discuss your availability, working hours and schedules with the clients when you enter a contract. I have experienced that mostly clients are quite understanding if we spell out the details before starting work.
Don’t ignore yourself during all this hustle, take good care of your physical and mental health. You are precious for your kids and family.
Best of luck.

You're so right. These boundaries seem to be pushed or just washed away in general with more of us working from home and, as parents, working at odd hours.

I think you could have a polite conversation about your working hours. You could also let clients know it could take you 24-48 hours to respond. I've found success in using auto-replys on emails (especially for the weekends, "I'll return your email on Monday during normal business hours" type thing). And, for my own sanity, I use the Do Not Disturb feature on my phone in the evenings so that I am not tempted to reply and set unrealistic expectations in the future.

Boundaries are a way to reduce our stress. As you say with pandemic restrictions, this has become so much harder for so many people! You have every right to set a boundary at the end of the day and not respond to further phone calls or emails. It sounds like you know exactly what you are needing to do in saying 'politely' to clients that my work day finishes at this time and I won't be responding to communication again until 'this time'. So I'd be interested to explore for yourself what happens for you when you don't respond immediately to your pushy clients and do prioritise your family instead? It is common to feel a sense of letting people down or that we are selfish when we prioritise our personal time over work but working from home with the pandemic is still work. So, it might be about being very clear about your start and finish time of work (in your own mind first and then to communicate this with clients) and to stick to those boundaries. When you are feeling pushed, remind yourself that you have worked during your hours set and if it doesn't suit you to respond, then give yourself permission to not respond and focus on your family -the ones that do care about your personal time!