小孩 (xiǎohái) means child or kid, a common and informal way to refer to young children. It is one of the most frequently used words for children in everyday Chinese conversation.
公园里有很多小孩在玩滑梯。
Gōngyuán lǐ yǒu hěnduō xiǎohái zài wán huátī.
There are many children playing on the slide in the park.
这个小孩才三岁,已经会背好几首唐诗了。
Zhège xiǎohái cái sān suì, yǐjīng huì bèi hǎo jǐ shǒu Tángshī le.
This child is only three years old but can already recite several Tang poems.
邻居家的小孩特别可爱,见谁都笑。
Línjū jiā de xiǎohái tèbié kě'ài, jiàn shéi dōu xiào.
The neighbor's child is especially cute and smiles at everyone.