This isn’t one of the busy bags I bought, but this is something I use for ds5. It’s good practice for forming letters, and he has enjoyed doing it multiple times (though not every day, or even every week) over the last year. The set is something I purchased: a book and 11 foam blocks, some curved and some straight. They are meant to be combined into the letters, and the book shows how it’s done. This has some novelty value for ds7, and is a little fun for ds2, but it’s really targeted toward the kids who are working on their letters. They can “write” without having to have the fine motor skills down, and it’s a fun thing to follow along with.
Of course, my boys tend to find new uses for all things as blocks, too:
All things are really meant to be used to build, right?
Here is the book: