I want my son to go to university instead of my daughter
Is there a reason why you are picking your son over your daughter to be more successful?
Yes, my son will need money to support his family and my daughter will have kids eventually and need to look after them.
That sounds a little sexist to me. Just because your daughter is having children, does not mean that she cannot succeed in her academic career.
I know that, I just feel this is the best option.
I doubt she would like your reasoning. Have you tried to see if you can afford to send both of them to school? They have programs to help with financial aid if that was a main concern for you.