Another vote for "no break-in required". It's a fair question - anything with mating metal surfaces still seems to benefit from some kind of gentle break-in period - but speakers don't really have any such surfaces to break in. The cone and voice coil are suspended by elastic components (surround / spider) and I haven't found anyone who claims that the properties of those components change appreciably in the first hours of use.
If the new speakers have a significantly different sound from your previous ones then it will take some time for that sound to seem "natural" to you, and if your family is used to action movies being played quietly there will be a break-in period there as well
