I found the same thing while pulling weeds from an area that had been recently mulched. I stuck the little thing in some cactus mix, but I'm only watering when it's dry. I've only had it about 10 days, so it's too soon to tell. I'd avoid overwatering, the most common cause of plant death.

lgteacher - that looks like some type of cactus in the middle of a jade! Or some really rare new breed of succulent! LOL

~Erin~

lgteacher, yours is an Opuntia (or Cylindropuntia). It should be ok. Just keep it moist. They're pretty quick growers and can be pretty tough little guys. Just don't let it dry out too much or for too long.

kittikity, Can't really tell what yours are yet, but I would put them in some cactus soil as well. I don't usually use plain commercially sold "Cactus Mix" because if you look at lgteachers picture, you can see lots of organic matter, like small wood chips or twigs. Normally this is not good, but will help you keep your seedlings moist. Keep them moist. Not wet but moist. At this stage of life, they prefer high humidity. Many people grow their seedlings in plastic bags to keep them moist. I usually keep my larger seedlings (out of the baggie) in a large "tupperware" type container with the lid either partially or completely off, to maintain more humidity than just a pot sitting on a shelf. If they dry out too much and for too long, you will lose them :( I do have a friend that will put any small seedlings he receives or finds BACK into plastic bags. So,you could try that too. IF you happen to find algae growing on the top, put a fine layer of sand over it.
Would love to hear your progress and see how they all develop (both of you)

this is really interesting, i didnt even know cactus seeded themselves, i thought they just grew offshoots like, or 'dropped' smaller parts to root themsselves,,
my sole cactus recently had pups, and i just plucked em off, stuck em in some gritty, and started misting them every 7-10(20?) days,, theyve grown some, i (think?) misting just encouraged 'hair' growth more than anything? lol but im sure they werent over-watered. :)

and it Does look like that last one has rooted itself into a crassula! ...curious,

Kitty,
i would suggest less-is-more on watering, cactus can go weeks without water,
but note that (mine) are strictly indoor (Z 6A) i dunno what Z9 is even hehe
have you done anything withem yet?
Would love to hear their progress as well. :)