This is a great question because many parents don’t really think about brushing until much later than they should. We see many toddlers and preschoolers with cavities, and this is part of why that happens! You should begin “brushing” your baby’s gums with a clean cloth at around 3-4 months old to keep the gums clean and ready for baby teeth. Once those teeth begin arriving, you can continue to use the clean cloth but will want to transition to an infant brush and toothpaste at around 6 months.
And don’t forget the floss! Use a flosser to begin cleaning between teeth as soon as your baby has two teeth that are touching.