Kits are no exception. If your product emits radiation in its final form it falls under FDA regulation.
Finally, if you build lasers for your own personal enjoyment or amusement they do not fall under the jurisdiction of the FDA. Use of the laser system may fall under the laws of your state or local constabulary.
That seems contradictory to me. What constitutes a 'kit', then? Could a domestic distributor get in trouble if they simple sold all the components required to build a laser, without selling the finished product?