Obviously, if they are learning the alphabet the following doesn't really apply; However generally, kids should choose their own path i.e pursue their own interests. As a parent all you can do is guide them, but they ultimately should choose what they enjoy doing. So, I don't think that Bitcoin should be forced on kids, just the same as anything else shouldn't.

As for this particular book, it just doesn't seem appropriate for all of the reasons listed above. You want to make sure that your kid is going to have as easy time as possible in school, and the alphabet isn't something that should be taught with Bitcoin.