I had this happen to ducks in my pool. Momma was honking and crap and they couldn't get out. I have no clue how long they where in there since I was at work all day.
But the little guys looked so tired when I found them. I had to figure out a way to get them out. I tried a net but no go, tried boards, and whatever else I had laying around..
Finally I had to do something like this video, built them a type of bridge to get out. Took them a good 1/2 hour to figure out what to do but them got out and momma led them away never to be seen again.