1. Plan specifics and next-steps while watching the kids. This is not to say you should ignore them or anything. An hour of dedicated play with the kids is usually followed by an hour of them playing with each other or doing something independent quietly (super important skills for them to learn IMO). When they are watching Sesame Street or playing with each other I have a note-taking app and Google Docs on my phone. I can plan next steps, write content, manage the project's social media, etc. from basically anywhere while still keeping an eye on the kids. I also make and maintain a TODO list broken down into bite-sized tasks in the note taking app (the default notes app that comes with Android). Using a phone in this way is more rewarding than surfing Reddit/HN anyways, and it will fundamentally change your relationship with your phone for the better.
2. Since most planning is already done (see step 1), when I have dedicated time to work on the project I already have a list of bite-sized tasks I can accomplish. Doing even one tiny task a day adds up way more quickly than you would believe. e.g. I do furniture, so on one day I photograph a completed chair, another day I cut fabric for cushions, etc. Maintained over the long-term, this adds up to a ton of progress without burnout. My guiding philosophy for this is "consistency + effort = improvement".
This system also works great for people with long commutes (assuming you're not driving)!