Contractures are the chronic loss of joint mobility caused by structural changes in non-bony tissue, including muscles, ligaments, and tendons. They develop when these normally elastic tissues are replaced by inelastic tissues. This results in the shortening and hardening of these tissues, ultimately causing rigidity, joint deformities, and a total loss of movement around the joint. (AAPMR)
The most comprehensive resource I have found that is accessible and realistic is the FREE Disabled Village Children's guide. The drawings aren't great, but the information is solid and it's written for countries without the resources available in the US, so you can do all of their suggestions at home and substitute any equipment you do have.
Passive stretching has recently been questioned in the prevention of contractors, but the American Academy of Physical Medicine and Rehab still recommends stretching regimens. Contractures and their mechanisms are still not well understood, and it's difficult to conduct research because contracture types and causes vary drastically. The good news is all of these prevention strategies are accepted as methods to prevent contractures, but they also help with so many other things: joint integrity, bone density, activity, mobility, independence and pain management.
Contractures can be incredibly painful and detrimental to quality of life. Spend too much time in one position and contracted muscles can get stuck in their shortened position. To a lesser extreme, think about everyone with "text neck" and kyphosis. Frequent, prolonged time spent in any position and the body adjusts especially when accompanied with weakness of opposing muscles. There are so many little things you can do during the day to help prevent your child from being in one position too long as well as supporting children in stretched positions with proper alignment. You can also work on stretching when changing, transferring or diapering.
Disabled Village Children A guide for community health workers, rehabilitation workers, and families
PART 1 WORKING WITH THE CHILD AND FAMILY: Information on different Disabilities Recognizing, Helping with, and Preventing Common Disabilities
Chapter 8: Contractures