missing money mystery

Rey was counting his savings last night when he discovered that 1 coin was missing.
"Mummy, 1 coin is missing! Who took it?"
It was the big 500 yen coin I had given to Rey earlier. My intuition told me that it is papa, because I heard him meddling with the piggy bank in the room.
Assuming the role of the detective, I announced' ""It must be papa because I heard him shaking your piggy bank."
Rey was shocked! So shocked that I have to lend him my 500yen coin to pacify him. Then seconds later, he was in deep thoughts. You know, when you're a mother, you seem to read your child's mind.
"You're wondering why papa would want to take your money right?" (Rey nodded sadly). So we went to question the suspect.
In the end the mystery was solved. Rey had earlier poured some money from papa's the wallet into his own piggy bank and the papa had mistakenly retrieved Rey's coin later. So, both parties fault lah!

Rey then suddenly came up with a downright silly idea of writing a message (in hiragana) saying, "No money in here!"
OH no!!! He's thinking like the silly guy in the Chinese sayings 此地无银三百两!

Now the piggy bank is surrounded by his collection of acorns. And to install further 'security', he put acorns in the piggy bank so it can "poke the thief's hands" when he tries to steal again.

Being kind, he made papa write the silly message and pasted it on the wallet too.