Based on the Tagalog sentence your friend provided: "Ang pusa ko ay kakapanganak lang nang limang kuting." This translates to: "My cat just gave birth to five kittens." So, your friend is talking about her cat, and the cat just gave birth to five kittens. If you're congratulating her on the new babies, it's likely she's referring to the kittens as her "new babies." Therefore, there are 5 new babies (kittens) to congratulate her on. You could say something like: "Congratulations on the five new kittens! They must be so adorable!"