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?

For the first 5 months I used wet cloth to wipe baby's tongue and gums. After that I used Pigeon Training Toothbrush set that comes with 3 Training Toothbrush Lesson 1, 2 and 3 and they are BPA Free and thus safe if baby bites on them. You are read up more on Lesson 1, 2, 3 rationals behind the designs of toothbrush from here http://www.pigeon.com.sg/product_uri/oral-care/training-toothbrush/lesson-1-2-3-set/