September is the starting of winter in India. Gangtok is called as Himalayan range of Sikkim. Here are some places to visit with a baby in Gangtok Ganesh tok
Himalayan zoo
Lingdum monastery
Flower exhibition Khecheopalri lake. Shillong is called as Scotland of east in the state of Meghalaya. Filled with rich history here are a few spots to visit with a baby
Elephant falls
Air Force museum
Hydari park
State and don bosco museum. I would suggest Gangtok.