I think something that can be confusing for some people is when unschoolers talk about "following an interest." I think they imagine that the child comes to mom and says "I'd like to learn about baking and money today," and then they sit down together and pour over information, do worksheets, maybe a field trip. While E has told me what she wants to learn about in so many words, that is rare. Usually I pick up on her interests through our conversations and if we can't look up the answers to her questions right that minute, I write them down and we do things later. Also, I bring a lot of things into her world that she didn't know existed, because she can't possibly be interested in them if she doesn't know they exist.
For example, a few weeks ago some kids came to our door offering babysitting and dog walking services. I politely declined since we don't have a pet and I won't be leaving my kids with 8 year olds, but I told them that I was impressed with their desire to make their own money. E asked how she could make her own money like those kids were doing and we started brainstorming some ides. She settled on baking and selling apple pies. I invested $10 into her business to buy the ingredients and together E, L and I made 2 apple pies. Then we put the pieces on individual paper plates and put them in a basket. She walked around our neighborhood and sold them to our neighbors for $2 per slice. I hung back while she knocked on the doors by herself, told people what she was doing and offered them a piece for "ONLY $2 each!" which people found cute and she came up with herself, little saleswoman. After paying D and I back with slices of pie, eating a few themselves, and getting a few tips, they made out with $24.
She said that was "WAY BETTER" than waiting to get the $2 we give each of the girls every week. She spent $10 of it to buy a jewelry making kit, because she wanted to continue her business venture and sell jewelry. The rest went towards fun at the county fair.
All of this came about because she made a little comment about wanting to make money too, and I utilized my adult knowledge and resources to help her run with it.
If you think your kids have no interests besides playing, just start talking to them! I can't even keep up with all the possible interests there are to learn here. In the last two days I've written down just a few of the many things that have come up in conversation:
How deer hide their babies until they lose their spots, where deer live and what they eat
Why magnets stick to metal
What a curtsy is called and the difference between a bow and a curtsy
What security guards do
The weather in the the antarctic
The arctic, Eskimos and igloos
Where Alaska and Canada are located on the map in relation to California and Oregon
Dinosaurs, carnivores, animals hunting
Nerves, brain, heart and how our bones protect our vital organs
All of these things are conversations that create learning in the moment, as I answer questions and provide new information, but sometimes they are 2 minute exchanges, barely a blip on the radar of our day if I'm not paying attention. I do try to pay attention though, because they are also interests that can be explored further. I figure if my kid is asking, she's interested! Now when I provide more information or a project or related trip later on, if she no longer cares about that topic, she'll tell me and I'll respect that. But that happens very, very rarely.
I don't say "I'm going to teach you about XYZ now that you expressed an interest in it," I say, "Hey look at this video of deer that I found" or "Remember last week you asked about what security guards do? Well I just met one and he can tell you about his job."
It's all about being engaged, interested in them and open to whatever comes up.