At what age do you start brushing the teeth of your children? Do we need to clean their gums before they even begin to have teeth?

Can start brushing the teeth once the first teeth erupt. But i clean my girl’s gum and tongue twice a day, since she’s newborn. Cause everytime after latching, will have milk residue stuck on the tongue also. Cannot don’t clean. This kind of silicone finger toothbrush very handy. The “bristles” can help clean the milk stain. But it’s also not too rough. When baby is teething, can also use it to massage their gums.