5 Y.O. 'Toddlers' Star
Gets DOWN Inside Nightclub
'I'm Sexy and I Know It'

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She's just 5 years old, but "Toddlers & Tiaras" star Isabella Barrett is already making nightclub appearances -- singing songs about her sex appeal -- and TMZ has obtained video evidence.

Barrett graced Libation NYC with her presence Monday night for a special charity fundraising event -- where she danced and sang along to LMFAO's "Sexy and I Know It."

In case you forgot -- Isabella is the same girl who said her fellow "Toddlers" star Paisley Dickey dresses like "a hooker."

Sure, the video's pretty cute -- but when we were six ... we sang songs from "Barney & Friends."