Maybe.... ..Thrush typically comes on the inside of the cheek, edge (not top) of the tongue, and inside of the lips and gums. It also does not come off with gentle rubbing. If that's what you see, thrush is likely. Fortunately, it's usually easily treatable, and not dangerous except in children seriously ill to begin with.
If there are white spots in other places besides the surface of the tongue, such as back of the throat or in your baby's cheeks its possible s/he may have a different type of infection. If your baby is having trouble eating, seems uncomfortable or is running a fever see your pediatrician.
Its possible. Whiteness on a baby's tongue is likely to be due to milk or thrush. If you can wipe it off then it was likely milk residue. If you can't, it may be thrush and you may need a prescription for Nystatin (anti-fungal medicine) from your pediatrician.