The chick actually recovered initially and was being fed by the parents but sadly drowned on its second attempt.
The other two chicks made it out but have since disappeared, despite the parents still being around; so it's feared that they may have been taken by predators or also drowned.
The young birds would normally still be very visible around the nest site for a week or so and very much dependent on mum for food.
The fact that they're not around, doesn't bode well for them.
I'll continue to keep an eye out for them though and let you know if we have a happy ending to this story...