An easy, not much equipment needed, activity is drawing. What I like about it is that it incentivizes visualizing things (not everyone can, and that is okay, drawing what you are looking at can be fun too!) and since I generally was not great at drawing nobody felt they were too "bad" at it to participate.
A program the girls took advantage of was Reikes Nature studies. One of the things they do is catalog as many things they can see at a nearby wooded park. When I read Feynman's discussion of how the ants became a source of fascination for him I realized that there are zillions of questions right in front in our eyes if we think about it. Or perhaps more accurately wonder why things are the way they are.
David Macaulay has a great book called "The Way Things Work." (and it has funny illustrations of mammoths figuring things out) Reading it together and talking about how things work led to interesting questions which led to interesting projects to see if we could answer those questions.
And generally "active reading" where you read together and talk about the characters in the story, what they might be feeling, why they might be acting the way they are, and how things might be different if something happened in a different way than it does in the book.
Perhaps the best idea to be genuinely interested in what they are interested in, rather than trying to get them interested in something you are interested in. That may seem obvious but it wasn't to me at first.
My eldest and I started doing piano lessons at that age, in part because the music was interesting and in part because I always wanted something "safe" we could talk about (and music was always a good topic of conversation).