Hi Swanlover and a warm welcome from all the Staff and Moderators.
I can't really answer your question and it may depend on which species of swan you are referring to. I think our Mute Swan males will drive, their young away before the start of the next breeding season, but they wouldn't normally kill them. They would, however, fight to the kill of intruder into their home breeding patch.
It would maybe be an idea to post in the Bird
Behaviour forum, where more people with the expertise on this might be able to help you.
I'm sure you will enjoy it here and I look forward to hearing your news.