I, too, have not heard of any laws which make human cloning illegal. As the other posters point out, the discussion of the idea is very controversial. As a parent, I do not know if I would be willing to do what has been mentioned in the previous posts. My fear, is that once it has been done, where does it stop?
Science has not currently progressed to the point of being able to clone humans. However, there are still donor children. Often these children are conceived through invetrofertilization. Doctors select the embryo that are genetically compatible. The cord blood can them be used to assist a sibling in need. Personally, I'm not sure how I feel about this. I can't imagine having a child simply to glean genetic materials. However as a parent, I can understand wanting to do whatever it takes to save your child.
Picoult's excellent novel is based on a number of true stories of parents having another child specifically to get stem cells to treat a child they already have, including the famous case of the Ayala family in 1990. There are no laws in the US banning child donors, but there are ongoing discussions about the ethics of this idea. The American Academy of Pediatrics published a study last year stating that using a child's hemapoeitic stem cells to save a sibling is ethical if certain conditions are met. However, siblings are not always a perfect match; hence this question about cloning.
At this point cloning of humans has not been done, and we are very far from being able to consider cloning a solution to the need for organs, bone marrow, etc. For one thing, creating a clone would take at least nine months, and in many cases an individual who needs a donation of anything does not have nine months to wait. Cloning success rates for the animals we have cloned are very low, so in reality cloning a human would probably take considerably longer than nine months.
The Human Genome Project has an excellent summary about the current state of the science of cloning at this link.
I know nothing about the legality of such a decision, but as Jodi Piocult's novel My Sister's Keeper shows, the ethical implications can be devastating for families. As a mother to four very healthy, robust children, I hope I never have reason to face a decision to have a "donor" child. I would like to say that I would never subject a child to the medically invasive procedures that he or she would undergo for the sake of a sibling, but if the technology existed and it was a legal procedure, I just don't know, which is why I hope such an option is never a legal possibility. All other donors have to provide consent, but a child would have neither the option nor the mental maturity to make such a decision. That is a position I would never want to be in as a parent - sacrificing one child for the sake of another.
There are no laws (on the level of the federal government in the US) banning cloning of human beings. However, at this point, there is no proof that a human being could be successfully cloned for any purpose at all. Given the ban on federal funding for stem cell research, it is unlikely that the sort of thing you are suggesting here would be approved even if it became possible.