They're millipedes. They don't do anything harmful and just nibble on rotting vegetation bits. They probably will disappear after a while. If you want them to stay in their pot, you can put a ring of insecticide around the edge of the saucer (or just petroleum jelly although that can get goopy) or put the saucer in a larger saucer full of water, like a moat.

They don't fly, they aren't fast, and any invasion of other plants will be a lucky event for them. They are also cute and totally safe for kids to play with gently*. (I don't recommend playing with centipedes, but once you get familiar with the looks of millipedes and centipedes, you won't mistake them.)

*I have been informed that the millipedes would rather not be played with. :P

The 2 pairs of legs per body segment in your pictures indicates millipede, as Fori has correctly IDed.