Hollo, it IS hard to do! I have the same problem, especially with Tom. But it is important to try and brush every surface of every tooth. So how long will really depend on how many teeth I guess. Different dentists will give you different opinions on when to start using toothpaste, (we have gone with around 2), but at any age the mechanics of the brushing is important - that is the physical brushing of the brush against the tooth. I wish I could give you some better advice on HOW to actually achieve this with a squirming reluctant child, but really for us it has just been patience and persistence. Often tag-teaming helps - one parent with the toothbrush and the other distracting. GL with it!