Yes, seems you all are having a rough time, but this happens when predators, domestic or wild attack other species, especially birds. The abandoned cygnet may be injured or too little (the runt) and could not keep up. The mother is not going to risk the family's or her life for a sick, injured or weak offspring that cannot keep up. To do so, only invites more predators to follow and attack the entire family. Glad you found a rehabber, but if it is very young, it's survival can be tenuous. It will never be able to live in a free setting and must live in a safe captive setting. Humans cannot teach it to be a swan or learn how to escape predators. Only the swan parents can communicate this vital info. However, thanks to you and your family's care and attention, he has a better chance of survival than he would have trying to survive on his own. Thank you for caring. The Regal Swan