Closest I've come to having to draw...

[BigStick]

I'll agree with suntzu, once the animal gets too close you would probably need to seperate them from family member before shooting. Once they make contact it would be a hard choice wether to get close enough and carefull enough to make a clean shot with no danger of hiting kid, or to just engage the animal physically. A swift kick might be safer for the child being attacked.

Followed up by putting down the attacking beast once they are seperated.

[DefensiveCarry.com]