The fair opens up after you here Grandma Ruby talking to Mr. Bradley. You can do all the fair achievements during this time. I recommend waiting until later on into the game when Miley goes around the fair to collect stuffed animals. You are required to play these then, so waiting won't hurt.
The frog game requires you to land on the lily pads. Each one will give you different points. Move the
to aim the launcher and then launch by pushing forward on the
and then pulling back.
My tip would be this. Barely push the
forward. Then pull back. This will hit directly in the middle easily. The game layout changes so if you get a bad set-up just try again.