The 17-year-old reality star has reportedly been dating Tyga for several months, and has taken on the role of a parent to the rapper's two-year-old son with former fiancée Blac Chyna.
A source said: ''Tyga pretty much raises King Cairo and Blac Chyna is only a part-time mother. Kylie has taken on a role of second mother to King, but she is in no way prepared to handle the role.''
However, doubt has been expressed over the 'Keeping Up with the Kardashians' socialite's ability to look after the tot, because her own mother Kris Jenner was not a ''good role model'' when she was growing up.
The source told PerezHilton.com: ''She does not know the first thing about being a mother because she really has had no good role model to learn how to be a mom.''
The couple - who were spotted at Disneyland in California with King earlier this week as they attended the birthday party of North West, Kylie's half-sister Kim Kardashian West's daughter - have reportedly angered the boy's mother though, who is unhappy about the pair's relationship.
A source previously said: ''Blac told Tyga that she does not want her son to even be around Kylie, but there is nothing that she can really do to stop this.''
Former Bengal Lancer Harry Sullivan, aka From The Tiger's Mouth, has just released his first solo single - 'Morning News' under his new moniker.