Unless you think or see the little guy making vent/vent contact, it's probably harmless, and if the female has bonded with you rather than another bird, pretty unlikely she'd bear any offspring. I'm sure some birds will reproduce having bonded with humans, but from what I've read, it's not very likely. (Accidents DO happen)
On the other hand, you are wanting to stop something that is a natural process of both birds. One question.. is the female actually trying to mate by raising her tail, getting in a somewhat horizontal position and making little squeaking sounds? If not, she's just tolerating the juvenile, and not interested in making babies.
Should she lay an egg or eggs, do not remove them until she gives up on them, or she will just lay more to replace them. Supposed to take about 21 days give or take, but she might give up sooner. You could always take them and boil them, then give 'em back. Might prevent a broken egg.
Again, it's a natural behavior, and I'd not try to stop it, but would also try some other methods of control over the female, like changing stuff around in the cage, moving the cage to a different spot, keeping the cage dark for 12-14 hours. Lots of other things to try as well. Maybe you can provide more background on her.. is she bonded with you? How long have the pair been together? Are they bonded, or attempting to? Mutual preening?
cheers!
Sam
