When someone experiences acute back pain often times it is during very simple, usually routine movements. You may hear, "I was just reaching down to pick my book" or "I just closed my car door" or "I just sneezed". The reality of these cases is that it wasn't that movement that created the injury; it was a series of unsupported movements leading up to it.
Think about what you need to do when you are attempting to break a twig. Usually, it takes a little work...you bend and twist it, and then bend and twist it some more. It usually doesn't break with one movement. When you move through your world without core engagement to support your spine, you are simply "breaking the twig" over time and eventually, pain makes its appearance. If you are awake, there should be a slight contraction of your entire core (abdominals and back) for stabilization and support.
Moms and Dads, your physical responsibilities when taking care of your children can truly tax your body. Vow to pre-load your trunk with an anticipatory core contraction before most movements and STOP BREAKING THE TWIG!