Breastmilk is the best source of nutrition for infants, including infants whose mothers have confirmed or suspected coronavirus infection. As long as an infected mother takes appropriate precautions—as outlined in the WHO Europe position paper shared here—she can breastfeed her baby.
http://www.euro.who.int/__data/assets/pdf_file/0010/437788/breastfeeding-COVID-19.pdf?ua=1