You mean returning those products as return values of the product_ids computed function _return_product_ids. First of all a one2many it's not recomended at all for tgis because of the checks against the needed many2one in the relation table used to maintain the parent - child relationship, so better you switch to a many2many computed field.

In the computed function just return the ids of those products in the format of [(6,0,ids)] where ids is the list of those products id. Also note that the compute function only will be called when the record is saved.