You have my condolences for your bad experience. It's reprehensible that the mother would let her child take your laptop while she was sitting there, then look you straight in the face and claim to not know what happened to it! She's clearly shirking her responsibility, not only to monitor her child but to compensate you for the damage her child caused.

Thanks for sharing your story; it's a sad reminder of how inconsiderate our fellow passengers can sometimes be.