So they aren't allowed to do anything that allows them to feed their community? You have a broad definition of "technology."
I'm actually more interested in how they expelled their children from and kept them off an entire planet without using technology?
Same way Amish expell their children from their community. And those usually don't come back with bulldozers to iron the place flat.
It's just speculation, but I guess at first it simply suffices to say "We don't want you here." and they fly away with the ships they came here (I guess the Son'a ships are actually Ba'ku ships). And then they tried to live their lives in exile, and then got obsessed with staying young. And after that didn't work out, THEN they returned to get the radiation by force. Because that was their last option.
Well, the other option would have been to apologize for the attempted takeover of the village (the reason why they were exiled in the first palce) and set up another colony, but as stated in the film, they didn't want that. The Son'a wanted to be players in the galaxy. They wanted technology, they wanted contact with other species, etc...
The Ba'ku simply didn't want that, and that's their good right.