Children created as so-called "saviour siblings" to aid a sick brother or sister must be monitored to ensure their wellbeing, experts suggest.
Babies are being selected because they are tissue matches for existing children
The recommendation is made in a report on reproductive technologies by the Human Genetics Commission.
It warns that once a child has been created to save a sibling, there could be a temptation to view them as a spare parts bank.
But the HGC says "designing" clever or sporty children is not on the horizon.
A number of "saviour siblings" have been born, including two-year-old Jamie Whitaker.
He is a near-perfect genetic match for his older brother Charlie - now five - who has a rare condition called Diamond-Blackfan anaemia, which could only be treated with a stem cell transplant from a matched donor.
'Need for safeguards'
The HGC's report, compiled following a national consultation exercise, does not talk about individual family's cases.
But it does consider the welfare of a child born as a saviour sibling, as part of its analysis of developments in reproductive technology and genetic testing.
It says there is concern over the extent to which that child is used to benefit another person.
The report says: "Taking blood from the umbilical cord after birth causes no ill effects, but the removal of bone marrow is more controversial as it causes discomfort, although the long-term risk of harm is slight.
"However, once it is accepted in principle that children can be created to save the lives of siblings, perhaps more extensive - ie the donation of a kidney - or repeated tissue donations may be seen as equally permissible."
The report suggests it would be difficult to justify preventing parents who have a child with a life-threatening condition from attempting to create a saviour sibling.
But it says there have to be safeguards for family relationships and the wellbeing of the child in such circumstances.
The HGC said there should be research into the wellbeing of children born in this way.
The report also calls for research to look at the development of children born after pre-implantation genetic diagnosis (PGD) - where embryos are selected if they are free of an inherited condition.
But the HGC said it is concerned PGD should not be considered as "purely routine" and called for clear advice so that women understood clearly that they could choose not to have screening.
Baroness Helena Kennedy QC, Chair of the HGC, said, "With the accelerating pace of genetic research, the possibilities for couples experiencing fertility problems or families with a history of genetic illnesses are now considerable and increasing.
"However these new possibilities bring with them new concerns.
"We have to balance the need to assure reproductive autonomy - the rights of parents to make their own decisions - with the welfare of the child and the wider interests of society."
But Josephine Quintavalle, of the group Comment on Reproductive Ethics, said the potential impact of new technologies - such as those for saviour siblings - should have been thought of before.
"These issues are absolutely what we have been worried about. And they should be thought about before children are used as guinea pigs in a social experiment.
"We can't imagine what it might be like for children born in these circumstances, and what might be expected of them in the future."