It is not recommended to apply mosquito repellent with citronella on babies under 2 years old. For infants between 2 and 6 months old, it is best to avoid using products containing DEET. Instead, try to use other mosquito prevention methods such as avoiding early mornings and late evenings, wearing long, loose, light-colored clothing, and using a mosquito net. Once the baby is older than 6 months, you can consider using DEET products with a concentration of 10% or less, applying them to clothing rather than directly on the skin.