Measures to ensure medicines are properly tested for use on children have been agreed by the European Union.
Half of all drugs for children have not been tested properly.
Drug firms will get a six-month patent extension in return for researching the safety and effectiveness of their products in children.
Currently, more than 50% of medicines used to treat children in Europe have not been specifically tested on them or authorised for their use.
Experts said the new rules would improve safety.
As many medicines are currently only tested on adults, doctors are often left to guess what level of dose would be safe for a child to take.
However, this can be fraught with danger as children sometimes absorb drugs differently to adults, and can suffer different side effects.
Few pharmaceutical companies currently produce drugs aimed specifically at children because clinical trials are more difficult and take longer.
The new rules will cover all medicines still in the development stage and not yet authorised which pharmaceutical companies want to target at children.
To gain a patent extension companies will have to present a "paediatric investigation plan" for existing or new medicines.
This will be scrutinised by a committee of the European Medicines Agency.
Commission Vice President GŁnter Verheugen, vice president of the European Commission, said: "I very much welcome this landmark agreement.
"This regulation will improve the health of children by ensuring innovation in the development of medicines for their use.
"What we are trying to achieve is that all the medicines that we have in Europe are examined (as to) how they affect children, whether they are suitable for children or not."
Rosie Winterton, the UK's Health Minister, said: "This regulation will help to ensure that we have safe and effective medicines specifically formulated for children."
Kent Woods, chief executive of the UK's Medicines and Healthcare products Regulatory Agency (MHRA), agreed.
He said: "The new regulation will ensure that medicines will be available to children in appropriate formulations."
It is expected that the regulations will become law before the end of 2006.
A spokesman for the British Association of the British Pharmaceutical Industry, described the new rules as a "great step forward".
"Research into children is difficult - differences between each age group are great, the numbers of children with a disease may be small and as they are growing they are constantly developing.
"All of this combines to make getting meaningful clinical trial results for children challenging.
"The incentives the EU have announced will enable companies to devote the large resources necessary to overcome these challenges."