My wife asked me this question. Yes. My wife. She's abnormal. Surprised?
She also fed me a couple to get me started. "Cleaning the garage," was the funny one.
Here's the thing. I don't think this is a particularly funny premise. Don't get me wrong; this is like my go to joke, taking something someone says and framing it in a dirty way. It's just that I don't get the mom part. Any one of these jokes is funny because it sounds dirty in a sex-way, but to get mom specific? You could clean the garage out with anyone, or on your own, even.
But I'll take the challenge and try to come up with at least one that's particularly mom specific.
Suck on her tit for sustenance.
Short Answer: Moms don't really do anything that Dads, or other family or friends don't also do. Tits for free is the only one.