他只是一个小孩子，很多事情都不懂。

Tā zhǐshì yí gè xiǎoháizi, hěnduō shìqíng dōu bù dǒng.

He's just a kid, he doesn't understand a lot of things.

我只有一个孩子。

Wǒ zhǐ yǒu yí gè háizi.

I only have one child.

我只吃了一片面包。

Wǒ zhǐ chī le yí piàn miànbāo.

I only had one piece of bread.