When you think about it, kids lives are packed full of boundaries. They're living in a world that's too big, too complicated, full of assumptions they don't understand and expectations they don't even know exist until someone tells them they've failed. A lot of unschooling is actually about helping kids find ways over and around and through boundaries so that their lives are easier. You almost certainly do some of that already - every time you pick up a kid so they can see something, you're helping them around a boundary.
One of the biggest boundaries for little kids is that they're little kids. They struggle to communicate because their brains aren't fully developed, they don't understand their own feelings, and the world keeps throwing them curve balls. A young child who is, for instance, hitting, often doesn't need a boundary set for them - they're desperately trying to communicate that the darn world is broken again. The toy got taken! The dog won't do the thing! The cup fell! I don't remember which way the shoe goes! They need help navigating the boundaries that are in their way - help understanding, help not getting into that situation in the first place, help change gears, help understanding what's going on. And a lot of that help happens before the child runs into that boundary in the first place. So as a parent, part of the process of helping kids deal with boundaries involves learning to be proactive - thinking and planning ahead so that our kids don't run into so many walls.
That may sound counter-intuitive - how will kids learn to deal with those walls if they don't run into them? But a lot of those walls are developmental - they go away. Most kids just plain grow out of the hitting stage as they get used to uncomfortable feelings and learn to predict human behavior a little better. Others are a lot easier to navigate when they're just little barriers - dealing with one or two new people is less overwhelming than ten. We can look for ways to keep barriers small and manageable so that kids have a chance to think and learn how to navigate without getting overwhelmed.
If this isn't sounding like the kinds of boundaries you have in mind, then you may be confusing boundaries with a sort of soft-edged version of rules. "The boundary is: no jumping on the couch." But seen another way, you've got a kid who needs a bunch of big muscle movement and the real boundary is that you don't feel comfortable with the couch being used to meet that need. That might be a boundary you can stretch or even get over - some boundaries really are just in your head. Or you could look for other ways to meet that need that don't involve the couch - a mini trampoline, some special cushions just for jumping. We had a designated "jumping chair" for a few years. The boundary of adults not being comfortable with ruined furniture didn't go away, but we found a way to deal with that boundary that wasn't all about finding the perfect way to say no.
A lot of deschooling for parents involves learning to do this kind of problem-solving so that "boundaries" aren't end points or road blocks, but opportunities to try something different. At first it can seem kind of overwhelming - a learning curve is a kind of real life boundary! But with time and practice it gets easier.