We never show mercy to bad people.

我们对坏人是决不容情的。

Please show mercy to the child.

请对这孩子仁慈一点。

I pray you to show mercy to the child.

我恳请你对这孩子仁慈一点。

My friend pray you to show mercy to the child.

我的朋友恳请你对这孩子仁慈一点。

We should never show mercy to a fraud among friends.

欺诈行为，我们绝不能心慈面软。