Is that like some kind of magical transformation of work into joyful leisure time based merely on genetic relatedness to the child? Sounds like something you ought to write up for a journal as it's certainly novel
There is a huge difference in looking after other people's children because you are paid to do so, and looking after your own. I actively choose to spend time (yes, my leisure time!) with my dd, because I love her and find her good company. I would not generally choose to spend time with other people's children.
I'm not denying that caring for your own children can involve a lot of work. It can, of course, be very hard work, especially when they are very young. But looking after your own children is a labour of love, not a job.
If you don't consider it to be a joyful way of spending your time, then perhaps you are not cut out to be a SAHP after all?