Getting a list of the contents of a field for all rows of a subform

Getting a list of the contents of a field for all rows of a subform

Hi, I want to make a field in the parent form which lists of the product names fields in all the rows of a subform

So if someone has bought a TV which is one row, a stereo which is another row and a microwave which is another row the parent form's  field would return "TV, Stereo, Microwave"

How'd I do that - I can't think of a search that doesn't use the word 'list' which gives me the wrong sort of answer

thanks