Too many children's drugs have not been properly tested, a report says.
Half of all drugs for children have not been tested properly, the report says
The House of Lords said 90% of medicines for new born babies and 50% of those aimed at children are untested after collating evidence from doctors.
The warning comes after the EU proposed a law requiring firms producing adult drugs to test if they can also be used to treat children.
The Lords report said the EU plan was right, but care must be taken on drafting the guidelines for testing.
Baroness Thomas of Walliswood, chairwoman of the Lords EU Sub-committee on Social Policy and Consumer Affairs, said: "It is worrying that so many of the medicinal products used by our children have not been properly tested to ensure the appropriateness of their use.
"Children are not simply small adults."
She said the guidelines for the law had to ensure "ethical considerations" were fully considered over testing in clinical trials.
The Lords report recommended issues over child consent to trails, access to research databases and the effects of drugs on different ages would all need to be covered by the guidelines.
It also said all drugs - prescription and over-the-counter - needed to indicate their suitability for children.
And it warned it was impossible to judge how well the law would work and called for a full review within a couple of years of implementation.
If the law is passed, it is likely to come into force in 2007. The UK government has already said it would adopt the legislation.
Professor Sir Alan Craft, President, Royal College of Paediatrics and Child Health, agreed better testing was needed, but urged parents not to be alarmed.
"We welcome the report from the House of Lords. It highlights once again that the majority of medicines given to babies and children are unlicensed. "Better testing would however result in a better situation for children. This should not alarm people, as the unlicensed medicines are prescribed by doctors with experience of working with children."
And Shadow Health Secretary Andrew Lansley said: "We need to ensure maximum safety for children's drugs. Equally it is difficult to conduct the very clinical trials on children needed to improve safety."