If your 17-month-old baby is reacting a lot to mosquito bites, you can try applying an oat-based cream like Aveeno as a primary treatment. You can apply it as often as needed throughout the day. If there is itching, you can consult a pharmacist to determine the appropriate dose of antihistamine for your child's weight. If the situation persists for more than 5 days after the last bite, worsens, or if other symptoms occur, it would be advisable to seek medical attention.