Since both variables are continuous, u can use the Pearson correlation coefficient. The higher the value, the more related are the two variables. Most probably; as one increases, the other increases as well (i.e. some positive r). So u need to see some high or medium-sized r (> 0.3) and it has to be significant (p-value < .05).
But be careful, a high IQ of the mother did not necessarily cause the high IQ in the Son. Nor the low IQ in the mother caused a low IQ in the Son. << NO Causal Relationship can be proved through your r >>
Causal relationships can be only examined through experimental designs, where the researcher can manipulate the X (independent variable) and notices the change in Y (dependent variable) after that.
