I would give them a light rub over with a scouring pad and see whether the rust was actually bubbling the metal or not once you get past the surface. If it isn't you can use a metal scourer to get simple rust spots off but do it lightly and then you can use a light grade sandpaper all over - just ever so lightly. You can then coat with a clear lacquer or similar if you think they'll catch after having been sanded. You can get spray lacquer of course. You just need to try and ensure a coating is even.
If the metal is really bubbling I would probably use them for garden stakes.
There ARE rust chemicals of course - same as used on cars etc but they're pretty volatile etc and I would avoid. The lacquer is good in the sense of preventing air getting to the metal which in part causes the rusting - like sea air etc. I think some really old metal needles were alloys and just not that strong etc and they were susceptible to rust.