These are baby opossums in the pouch. When born only the head & arms are formed. Up to 20 or so are "born" then they have to climb up to her pouch. The rest of the body develops in their mom's pouch IF they make the climb to it! There's only 13 nipples, so whoever gets there first will survive. You can fit 50 babies inside a teaspoon, that's how small they are when they come out of the birth canal 13 DAYS after she gets pregnant. They will stay in the pouch for 2 months. Opossums are the only mammals that do this in North America.
And did you know that opossums can't get feline/canine distemper or rabies.They will kill all rats, mice, bugs and even copperheads, cottonmouths and rattlesnakes around your house? The poison from the snakes can't kill the opossums. As long as you keep your trashcan lids on good & tight they will not get in your trash, but rid your yard/under house of yucky pests. They will not attack unless you corner them and even then they would rather run away. They will hiss & show teeth but its 90% show. They only have a 2-3 years life span :(