Years ago, as a wildlife rehabilitator, I rescued a litter of baby possums from the pouch of their mother who'd been hit and killed by a car a minute prior. They were really tiny, about the size of peanuts in the shell, pink and hairless and beyond helpless...
I fashioned a miniature feeder with an eyedropper and managed to keep five of the them alive with milk replacement mixes. As they grew into young'uns they started looking more and more like the ones in the picture you posted.
One day I opened the lid of their box and got the most astonishing display of snarling, ferocious, angry hissing I had ever heard from baby animals. Gave me a whole new appreciation of the phrase "small but fierce".
But man, possums are stupid. They're SO stupid. Soon as I could let 'em go, I did, because they were so stupid they'd have ripped my hand off while I was trying to feed 'em.
[And thanks for helping to take care of critters in need.]