A world-famous American website for free educational videos, with clear visual examples and explanations. It's used by people all over world.
The maths videos are particularly useful to primary school children.

Grade 3 is Y4 level, Grade 4 is Y5 level and Grade 5 is Y6 level. There is also a section on 'Early Math' which can help children in FS, Y1, Y2 and early Y3.