Several argued it was not an age-appropriate decision for the young girl.
"Wow, kids this age put on nails in the USA..wow," a third person wrote.
"WAIT…does she have tips on!?! At that age I was lucky enough to wear eyeshadow," another said.
However, others were more kind about the choice.
"Her hair and nails are amazing," a fan pointed out.
Others requested that Penelope share a tutorial of her stylish look with her followers.
The Sun reports the account was also temporarily banned shortly after the pair joined the platform for "violating community guidelines", however it was soon reinstated. It is though the account was removed temporarily because Penelope is younger than 13.
It appears TikTok is the new craze among the young Kardashian clan - Kim Kardashian and her daughter North West launched their own account late last month.
Kourtney also shares two sons with her ex Scott Disick - Mason, 11 and Reign, 6.
The celebrity and founder of lifestyle brand Poosh recently got engaged to musician Travis Barker.
Barker proposed during a romantic beach moment featuring and extravagant display of flowers and an oval-shaped diamond ring.