2 sentences for 孩子气 (hái​zi​qì)

1. 他都已经三十多岁了，说话还是很孩子气。

   tā dōu yǐ​jīng sān​shí duō suì le, shuō​huà hái​shi hěn hái​zi​qì.

   He is already in his thirties, but he still talks very childishly.

   Source: Dong Chinese Dictionary

2. 过了这么多年，他身上的那种孩子气一点都没变。

   guò le zhè​me duō nián, tā shēn​shang de nà zhǒng hái​zi​qì yī​diǎn dōu méi biàn.

   After all these years, his childishness hasn't changed a bit.

   Source: Dong Chinese Dictionary