Britney Spears has definitely had a big influence on her niece Maddie.

The little 4-year-old cutie, whose mom is Brit's younger sis Jamie Lynn, is striking a pose ... dressed as Brit from her "Baby One More Time" music video. Lil' Maddie was in costume for "celebrity day" at her Catholic school.

Brit was only 16 when the video debuted on MTV in 1998. Time has definitely flown by!