In large/very large families, it is usually the youngest children who are the most affluent, educated, & successful. Youngest children in large/very large families are given myriad opportunities that their oldest & other older siblings didn't & never had. Youngest children are furthermore treated far more preferentially than their older siblings.
Youngest children in large/very large families oftentimes have it easier than their oldest & older siblings. Since oldest & older siblings have to curtail their education to supplement family income, there is money coming in & that money is funneled to the welfare of the younger children in the household. Also, there are parents who are more economically solvent by the time the youngest child comes along so many a youngest child in large/very large families grow up in better socioeconomic circumstances than their oldest & older siblings so college & other forms of advanced education are a possibility. However, more likely or not, it is oldest & older children who send youngest children to college.
Since youngest children are the most educated out of all of their siblings, it is not rocket science that they will have the better jobs, earn more money, & be inordinately successful. That is par for the course. Even if they are not college educated, youngest children in large/very large families have avenues to achieve success that their oldest & older siblings DON'T & truthfully WON'T ever achieve in their lifetimes.