Mr. Clark, adopted at the same time as the kittens, did that from the
beginning. Mind you, he did take on a martyred look when they nursed on
him, but he let them continue. There were times he'd walk by with a
kitten riding on his back.

He still washes everyone, and approves of my having grown a beard. I do
note that he's utterly fascinated with visiting humankittens.  He
doesn't mind sharing their bottle, but he's not demanding of it.

Little Bit introduced Rocky to her kittens one day when I had them
outside and Rocky came visiting. This was back when Rocky was about
3/4 wild, willing to come to me when he wanted food, but just barely
tolerant of being touched. I was concerned about how he would react,
but he plopped down and let them climb all over him. Of course,
there's a good chance that he was their poppa, since he was the
dominant tom in the neighborhood, and I didn't adopt LB until she
decided she wanted inside to have her babies.

It's also great/funny to watch when a d*g adopts a kitten. When I was
growing up our male daschund,Bobo, pretty much raised a kitten he
found dumped in the foothills. The kitten's eyes hadn't opened yet, so
the first four legged animal he saw was Bobo. It was hilarious to
watch Mittens, the kitten, try to nurse on Bo. Nothing can beat the
long-suffering look in a d*g's eyes when they put up with something
because their master thinks it is just so danged cute. Mittens never
did outgrow his love of Bo, and grommed him all his life.