Some kids are cum-resistant, which is a real shame and something that should eventually be cured through science and/or legislation. But for now, there are plenty of fathers out there who have to deal with a kid who does not take to cum naturally, who don’t inherently understand the importance of the scum that shoots from their dads’ nuts.
Fortunately, there are some methods that, though annoying, can work. The first step is, not surprisingly, force feeding. You can do this in any number of ways: holding your cock in his throat while you jizz, pinch his nose until he has to open his mouth and then make a direct deposit, or just sneak up on him when he’s sleeping or relaxing and shove it in. I do recommend however using a mouth spreader like you see above. This allows you to shoot come into his mouth from far enough away that he can see what you’er doing with his eyes, which is important for getting him on the right page.
Once you’ve done this enough, he will begin to dread being forced, and eventually you can offer him the opportunity to eat it on his own. He will most likely accept, as having it forced upon you can be painful and humiliating. Of course, it’s humiliating to sit there and have to contemplate how you want to ingest a bowl full of your swimming siblings encased in dad’s ball mucus, but that’s at least something he’ll feel like he has a bit of control over. And giving them just a tiny bit of control in their own rape is really how good fathering is done.