Remote work is killing my work-life balance

So I thought working from home would be perfect. No commute, more time with the kids, flexible schedule right? Wrong. Now I'm answering emails at 9pm, my boss thinks I should be available all day since I'm home anyway, and my kids don't understand why dad is in the office but can't play with them. I feel like I'm neither fully present at work nor fully present with my family. Anyone else dealing with this? How do you actually set boundaries?