A mosquito bit my baby on her breast nipple and it turn red n hard within 24hrs and a boil appeared. Can mosquitoes cause boils? & how to treat it?

Depends. The proteins in the mosquito saliva can cause and inflammatory reaction that causes an itchy red bump. Any insect bite can become infected especially if it is scratched open. Keep it clean with soap and water. Keep the child from scratching it by covering the bite or placing something on the child's hands. I recommend having it assessed by a dr for infection and need for additional medication.