You could get a Cream Legbar hen too, and your kids could collect the occasional blue egg, and you might just not incubate those eggs.
Or you could incubate some of the blue eggs, and not know which chicken will lay what color eggs (until the crests of the Legbar-daughters become visible).
Or...
If you just want healthy backyard layers, I would probably buy a utility strain from a hatchery for the parents, but buy at least twice as many as you expect to need. Any time you find one with any problem that affects their ability to be healthy and productive, cull that bird (either eat them...