About 26,000 children are taking part in a research project to find better ways of treating lung complaints in those born prematurely.
Doctors from Cardiff University want to investigate whether better treatment of babies born moderately early could improve their breathing in childhood.
Families will be asked to complete a questionnaire on their child's health.
The children involved will be those born both on time and prematurely.
Doctors will compare incidences of coughs, colds, wheezing and chest infections between the two groups to find out if both extremely premature babies (born at less than 28 weeks) and moderately premature babies (born between 28 and 37 weeks) are more prone to them.
Prof Sailesh Kotecha, who is leading the research with Dr Martin Edwards, said: "In Wales, there are about 35,000 babies born each year and from these about 2,500 are born prematurely.
"There has been a lot of research demonstrating the negative effects that extreme premature birth can have on the lung function of children, but there's limited data on the lung function of moderately preterm born children, especially as they grow older.
"We are therefore asking families for their help by telling us more about the breathing and health related problems of the child and also ask about the child's development and learning.
"This will help them establish if children born only moderately prematurely need to be followed more closely during childhood than has occurred until now."
Dr Edwards said 13,000 questionnaires would be sent out to every child in Wales who was born prematurely aged from one to 10, and a further 13,000 to a sample of full-term children born during the same period to act as a control group.
"This is an enormous task but it is very important to establish if children who are born prematurely even by a few weeks have ongoing breathing or developmental problems when they grow up," he said.
The results should help medical staff decide if moderately premature children need to be followed up or treated from an early age, even if they do not show symptoms of breathing difficulties.
He said earlier research on very premature babies had shown that quite often they did not show symptoms of breathing problems, but when their lung function was examined closely it was found that they did have issues.
He said at present there was no recognised pathway for dealing with moderately premature children in relation to breathing issues.