Here is the answer:
The lady should tell the crocodile: "You will eat my child"
*if the crocodile eats the child, then the lady is correct and the crocodile must give back her child right?
*but if the crocodile eats the child, the crocodile is contradicting what he just told the lady... because the lady just answered his question correctly. right folks?
SEE?? this just a simple paradox.. )