Assuming you paid your house-for-rent with your own money: that you worked for, as opposed to won at the lottery or from previous investments. In a sense, the family that is giving you rent money is only paying your work back… until that point where you get your full ROI (cost of the house + your own work + interest).

Beyond that, the only reason they give you more rent money is because you own the house. But you got your ROI so by now they have paid for the house. And yet it's not theirs, so they still have to pay you. And when they do, any additional money you get, you basically took from them. As for your son, who presumably did not work for the house at all, will definitely take money from people through that house. Just because he had the right dad.

Don't get me wrong, you investing for your son and securing his future is you being a good dad. You just can't wave away how the current system works: people who own stuff have the power to take money from people who don't.