In spoken german it is not very common to use the ending -lein. Often you can find it in older books or in poems. -chen is more common (Blümchen, Bienchen,...). Both endings belittle nouns. But in general we do not use both of them very often.

This ending makes the word sound a bit softer or smaller, like a pet name. In German two endings have such function: -lein and -chen (both can be used, but the last one is more common). Sometimes there is also slight difference in usage: Fräulein - not married woman Frauchen - pet name for a woman

"-chen" and "-lein" have the same function: they are diminutive endings. -chen is more common, and originally "-chen" is Northern German and "-lein" is Southern German.