Speaking from the pov of the one to do the humiliating, it depends on the situation.
If her brats are still young, and still sucking her tits almost as often as I do?
I'm cumming on her fat tits, specifically aiming to have her fat nipples dripping with my own milk. Even if she cleans them after, in her mind they'll never truly be clean. They'll always be stained by the feel, smell, and taste of my cum, and she'll always see her tits as my fuck jugs first and foremost, her family's milk producers a distant second, feeling perverse every time she uses them for their natural purpose. It will ruin the most important bonding experience that can exist between a mother and her son or daughter, and knowing I've broken that relationship before it even began, will turn me on enough to be ready to go again as soon I'm done smearing my cum all over her tits.
If her family are nearby? Like I drag her into the other room during a family Christmas or a school play?
I'm either cumming on her face, or cumming on her tits. Then I'm making sure she doesn't have time to clean herself up before she gets shoved out the door to face her family.
If it's on her face, then she's gonna struggle to wipe it off while anyone who notices, desperately tries to convince themselves they were wrong and at fault for even thinking that.
If I cum on her tits, I'm making sure it soaks through her top, and gonna laugh as her son and/or daughter goes in for a big mommy hug, and she has to choose between rejecting their hug, leaving them feeling unloved and unwanted, or accept their hug, rubbing her cum soaked tits all over them, and hoping they don't feel or smell it, and she doesn't leave them stained with my cum too.
Though the mom is the only one feeling humiliated there, not her son or daughter (untill I decide to tell them all about it 😂)
Also always wanted to make a mom jerk me off onto her kid's most treasured belonging. Their lucky t-shirt, the expensive telescope they worked their ass off all summer to save up for, a poem their first love gave them years ago, the trophy they're most proud of, the Teddy bear their grandmother gave them before she passed away. Then leave the cum there to eventually be discovered, leaving them wondering why the thing they value most in the world, is sticky, stained, and smells bad.