Children on Mars will not be as smart as their parents. Is this a true statement?
Artificial selection of the immigrants will create a particular sub set of humanity. But the effect of genetic mixing inherent in life will mix the genome of the children in ways that do not necessarily favor the same characteristics as their parents.
The very nature of intelligence being unknown and multi form, the immigrant selection might actually not select for some important aspect of intelligence. So it might make sense to add some randomness to the process by limiting the selection.
Anyway, it is likely that nepotism, inherited wealth and other forms of favoritism will skewer the selection process to the point it might not have any real effect.