Normally, it is the mother that takes the cygnets around the habitat, not the male swan. However, if she needed a rest, the male may have taken them to the other side. If there is another pond in the area or the male got disoriented, he may not find his way back.

If there is something wrong with the mother, then the male could take the cygnets away from her so that they do not catch an illness or have a predator follow her to the rest of the family if she cannot keep up or escape. Hopefully, there is nothing wrong, the mother just needed a little rest and the male took the cygnets for a while and you will see the family together again shortly. The Regal Swan