How big are the cygnets? Are they smaller than a duck? If so, then they may be in danger of predation. If they are larger than a duck, i.e., half the size of the parents, then, they may have been introduced to the pond at a young age.

If you are absolutely sure that the swan parents are not around and that the swans do not belong to anyone (i.e., they are captive and someone introduced them to the pond as cygnets rather than as adults), you need to let the cygnets get extremely close to you while feeding. You may need several people to help. Once you try to capture one cygnet, the other cygnets may scatter, so you will need to capture them all quickly. As soon as you can feed them close to you, wait until their heads go under the water for the food and then gently scoop them. Place the cygnets in a box lined with a towel or sheet and with adequate air, carefully watching the cygnets so that they do not get entangled in the sheet or towel.

NEVER place the cygnets on a slick surface such as slippery floor, newspaper, box bottom, etc.

Also, never hold the cygnets legs in a splayed position, i.e., legs outward as the cygnets can suffer problems with soft tissue injuries and these are extremely hard injuries to treat. Once in the box, immediately get the cygnets to a waterfowl rehabilitation center where an experienced avian (bird) veterinarian can look at the cygnets and place them in a safe environment for them to grow. The Regal Swan