Hi Joann,
If we let P=the original number of peanuts then we can express what happened as:
Child 1 took 1/3P so 2/3P remained
Child 2 took 1/4of2/3P or 2/12P so 2/3P-2/12P or 1/2P remained
Child 3 took 1/2of1/2P or 1/4P so 1/2P-1/4P or 1/4P remained
Child 4 took 10 of the remaining and there were 71 left so 1/4P-10=71
Solving for P gives P=324 which is the original number of peanuts in the bag.
The key here is to account for the remaining peanuts at each step.
Jim