The pair have had two previous births so I am not sure if they would be considered a "young" couple. Also, I can't see that they may be from the same couple but a different nest because all of the cygnets are of equal size. There has not been another swan in the area so also not sure this could be a case of a male swan mating with two females unless the other female was driven away from the area. Regardless of the how it seems as if the two clutches have "blended" and are being well taken care of. If you come up with any other possible explanations please let us know since this has stirred quite a lot of interest both at home and in the school where I work. Will forward photos when available if that will help.