Definitely a good idea to start cleaning them as soon as they come through. A face cloth seems to be a good option, or one of the tiny baby toothbrushes. They definitely don't need toothpaste at this age (truth be told, none of us really do!), so just give them a good wipe over.

I think once kids hit about one it's good to let them have some time with their toothbrush, to get used to doing it themselves. Make it fun, sing a song, whatever it takes! But all kids should have their parents 'helping' them until 7 or 8. Some even older! They have a go, and then you do the good clean. It's amazing the difference it makes, their little hands just don't have the dexterity to do a good job before that.