Leah Still -- DOMINATES RUNWAY ... At NY Fashion Week

Best video of the day ... 5-year-old Leah Still CRUSHING IT on a catwalk at NY Fashion Week last night ... with so much confidence, she even pulled off a SPIN MOVE!!!

Leah's dad Devon Still was on hand at the Kids Rock! event -- and captured the moment on his camera ... saying, "She was definitely feeling herself with that spin move."

As our friends at BSO pointed out, Leah wasn't the only celeb kid at the event -- Carmelo Anthony's son Kiyan was also struttin' his stuff on the runway!

#TheFuture