Yes, it is possible that the yellow/brown/white discoloration on your baby's tongue could be thrush. Thrush is a common fungal infection that can appear as patches on the tongue and inside the mouth. It can cause discomfort for your baby, especially when swallowing. If you suspect your baby has thrush, it's important to consult a doctor for proper diagnosis and treatment. They may prescribe Nystatin, an antifungal medication, to help clear up the infection. It's also important to take care of your own health if you are breastfeeding, as thrush can be passed back and forth between you and your baby. Treatments like Canesten may be recommended to help clear up any fungal infections on your nipples.