Here's what I did... as soon as I would open the game, I would select a child, then deselect them. I would then watch the water, but not click on anything. As soon as the fish would appear (which for me was by the dock as soon as the game would start up), I would click on the circle where you bring up the villager stats, and it would select the last villager I had chosen (the child) - grab the child and drag them to the fish. Success for me. I could only get one fish per day.

As far as the boulder goes, I have completed all puzzles, but no luck with the boulder covering the cave. I do have one more hour for my garden flowers to bloom even tho all puzzles are finished, so that is my only idea.