Wǒ yòu búshì sānsuì xiǎoháir!
我又不是三岁小孩儿!
I wasn't born yesterday!
Notes:
我(wǒ): I
又(yòu): to emphasize
不是(búshì): be not
三岁(sānsuì): 3 years old
小孩儿(xiǎoháir): child
Example:
A:先去洗手。
Xiān qù xǐ shǒu.
Go to wash your hands first.
B:我又不是三岁小孩儿。
Wǒ yòu búshì sānsuì xiǎoháir!
I wasn't born yesterday!