Post a Sign When You're on Duty
This is a critical tip for parents trying to work from home. Whether you are working in an official-looking home office or at a milk crate desk in the corner of your bedroom, make sure that there is a door between you and your treasured distractions (er, children). If your kids are older, this door is a great place to post your daily work schedule along with a number they can dial to reach customer service, i.e., your spouse's cellphone.
If you have younger children, you need to post a sign that can be easily interpreted by a toddler to mean, "I love you, but please go bother daddy." Try a large "X" or a color-coded system like a construction-paper stoplight — green means "go on in," yellow means "enter only if you are bleeding/vomiting," and red means "there is a monster behind this door." That guy doing an interview with the BBC from his home office a few years ago could have used this system.
This system is also valuable for the adults in your life who maybe don't understand that "at home" doesn't mean "watching Netflix all day and therefore very interruptible with every little thing that crosses my mind." Block out your work hours in your shared calendar, use away messages for texts, and let your mom's calls go to voicemail.