Trying to drop children in the pond or the sea always seems to create a mushroom or a bug/gem/other collectable item - have no idea why - its just something I tried messing around with and it virtually always happens!

It seems to work best when you wait until there are lots of sparkles at the front of the pond altogether, or in the sea - then attempt to drop the child in the pond 3 or 4 times in a row quickly and within 30 secs or so, a collectable item or a mushroom will appear (sometimes 2!)

...obviously, the children never actually go into the pond when you drop them, it just says "children can't swim!" but it is attemtping to do it that works!