Hi Rod
I believe it (the carrying of young) to be common behaviour.
I hadn't seen it before 3 years ago but have seen it in all (closely
observed) very young families since.
Never after ten days.
Have seen one adult carrying 3 young; and a pair fo adults each carrying
two young.
Have also seen it on land.
When i asked about it on the chat line about 3 years ago,
somebody
reported it as common behaviour for Mute Swans
I have lots of photos of this behaviour,
There are a couple of pictures on the COG Photo Gallery
roger