A family of six were rescued from a broken-down speedboat which was taking on water as it crossed an area between Caernarfon and Anglesey.
The RNLI team from Trearddur Bay said the two children and their father waded to shore after being picked up.
The children's mother was carried ashore by her husband.
But an elderly couple in the boat, one of whom could not swim, needed the team's help during the rescue near Llanddwyn Island on Sunday afternoon.
RNLI helmsman Leigh McCann said the boat had been passing over a tricky stretch of water even on a calm day.
He added: "It's easy to get caught out but they all had lifejackets on and had a means of contacting help."