You must use the children to pick up the mushrooms in waiting of the 2nd source of food, which is:

Don't forget that if your game is in 2x speed, your villagers will eat more than in 1/2 speed!

You may look in the Forums List » The Guides » Virtual Villagers 2: The Lost Children Guide »
General Strategy Guide
Then, if you want: Hints for the 16 Puzzles
And,if you need: [BIG SPOILERS] Detailed solutions for the puzzles!

Also, something very useful: Backing up and recovering savegame files

Good luck!