Here are some fun games to help you with Length!! Remember!
10mm=1cm
100cm=1m
1000m=1km
http://www.bbc.co.uk/skillswise/topic/length-and-distance
http://www.bbc.co.uk/schools/ks2bitesize/maths/shape_space/measures/play.shtml
10mm=1cm
100cm=1m
1000m=1km
http://www.bbc.co.uk/skillswise/topic/length-and-distance
http://www.bbc.co.uk/schools/ks2bitesize/maths/shape_space/measures/play.shtml

This funny video might help you to understand the metric system a little better!