Little kids absolutely love learning to walk, you can see it in their faces and their behavior. When they start walking, they are so excited and happy to do it.

After a certain point, performing a complex task subconsciously becomes routine and one needs to sort of “level up” to a more difficult version to notice the flow state. The subjective experience is that the activity “slows down” and feels easier, allowing your conscious mind to wander.

You see this even within sports, where the best athletes need the biggest races / competitions / events in order to feel the same way they did when they were younger learning the sport. The best surfers seek out the biggest waves, or the hardest moves, or both.

I suspect "flow" necessarily demands intense focus, so mundane tasks can't lead to a flow state. Focus is probably the wrong word since that suggests conscious control, whereas most flow seems to relegate consciousness to the role of observer. Two things seem to occur: intensity of subconscious processing, with an absence/minimisation of conscious processing. The task itself is important too, it has to be "important", typically something that requires a lot of practice with the goal of improved performance.

I'm a street photographer and absolutely get into a flow state when I'm out on a long photo walk. Even if I'm not finding the light I need and barely talking pictures I reach a state where I notice everything effortlessly and time slows just walking down the street. You become part of the rhythm of the city.

You might have a point about flow state from simple routine. It's relatively hard to get into a flow while programming but it's easy while in the shower.