You can bring your partner and children to the UK as your Tier 4 dependant if you are a government-sponsored student and your course is longer than six months or you are doing a postgraduate level course of 12 months or longer at a publicly-funded Higher Education Institution or a 'recognised body'.
You cannot bring your family to the UK as a Tier 4 dependant if you are studying an English language course, a course which is below degree level or an undergraduate course (except if you are a government-sponsored student).
For further information, visit the UKCISA website.
If you decide to bring your family with you when studying in London, it is very important that you plan and prepare for their move to the UK. In addition to ensuring you have the required funds and visas, you will also need to arrange accommodation, school or nursery places, and work opportunities for your family.