Hi raspberryroop:
For KS1 (Y1/ Y2):
BBC Learning (BETA) website: direct access to teacher's resources
www.bbc.co.uk/schools/teachers/keystage_1/topics/maths_ks1.shtml
just select concept you wish to work with in central menu
BBC Learning KS1 Bitesize - reinforcing through games:
www.bbc.co.uk/bitesize/ks1/maths/
For KS2 (Y3/ Y4/ Y5 & Y6):
Again BBC Learning (BETA) website: direct access to teacher's resources
www.bbc.co.uk/schools/teachers/keystage_2/topics/maths_ks2.shtml
BBC KS2 BITESIZE (intended for SATs prep in Y6, but useful all years KS2):
www.bbc.co.uk/schools/ks2bitesize/maths/
For KS3 (Y7 - Y9 ages 11 - 14)
Again BBC Learning (BETA) website: direct access to teacher's resources
www.bbc.co.uk/schools/teachers/keystage_3/topics/maths.shtml
Also BBC Bitesize KS3 www.bbc.co.uk/schools/ks3bitesize/maths/
If your 13 year old is past these and wants more challenge access KS4 materials on BBC Learning BETA:
www.bbc.co.uk/schools/teachers/keystage_4/topics/maths.shtml
and of course BBC GCSE bitesize: www.bbc.co.uk/schools/gcsebitesize/maths/
BBC does have a bitesize site for the Scottish Higher: www.bbc.co.uk/scotland/learning/bitesize/higher/maths/
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This website is a bit different - but is about the application of math to sport (which may be attractive, especially in an Olympics year!):
sport.maths.org/content/help#KS - shows content by Key Stage or sport (so a lot of options there)
KS1 work here: sport.maths.org/content/category/tags/KS1
KS2 work here: sport.maths.org/content/category/tags/KS2
KS3 work here: sport.maths.org/content/category/tags/KS3
KS4 work here: sport.maths.org/content/category/tags/KS4
KS5 work here: sport.maths.org/content/category/tags/KS5
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If your 13 year old will respond to videos better I'd recommend:
The Inside Maths series (KS4) on Teacher's Media:
www.teachersmedia.co.uk/series/inside-maths
Johnny Heeley's Master Class:
www.teachersmedia.co.uk/series/jonny-heeleys-masterclass
A world of maths:
www.teachersmedia.co.uk/series/a-world-of-maths
Teaching Pythagorus:
www.teachersmedia.co.uk/videos/teaching-pythagoras
In the Secondary Lessons Starters - there are a series of lessons about the mathematics of Durham cathedral:
hidden patters in Durham Cathedral: www.teachersmedia.co.uk/videos/hidden-patterns-in-durham-cathedral
finding the golden ratio in Durham Cathedral: www.teachersmedia.co.uk/videos/finding-the-golden-ratio-in-durham-cathedral
Symmetry & Circumference in Durham Cathedral:
www.teachersmedia.co.uk/videos/symmetry-and-circumference-in-durham-cathedral
Measuring heights in Durham Cathedral:
www.teachersmedia.co.uk/videos/measuring-height-in-durham-cathedral
The Floor Plan of Durham Cathedral:
www.teachersmedia.co.uk/videos/the-floor-plan-of-durham-cathedral
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Finally for your KS1/ KS2 children - if what they need is practice, but possibly best in game form - I'd highly recommend Tux of Math Command. This is free open source maths videogame roughly based on Asteroids. You can select the individual level and the type of problem to solve and then off you go.
You can find out more and download the programme from here:
tux4kids.alioth.debian.org/tuxmath/index.php
I'm sure there's tons more - but that's a start.