Some links that may be helpful...

http://commoncore.org/maps/math/video-gallery . These are short videos that explain some of the key math models used in the K-5 math modules.

http://www.engageny.org/video-library  . More videos. Use the search box to filter for just math videos.

http://www.engageny.org/educational-activities-for-parents-and-students. These are educational sites aimed at helping students work online to deepen their mathematical skills.

https://www.khanacademy.org/.  The Khan Academy is helpful as well.  Select “learn” then “arithmetic” to get to elementary math concepts.

http://www.engageny.org/parent-and-family-resources This link is more general, not just math, but has nice resources.