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.