“Ronnie” is a nickname applied to Ron Weasley by members of his family. Molly Weasley called Ron this when he was made Prefect. Fred and George made retching noises behind her. A few moments later she expanded on this with “Of course you can… well, I’d better get going if I’ve got a broom to buy too. I’ll see you all later… little Ronnie, a prefect! And don’t forget to pack your trunks… a prefect… oh, I’m all of a dither!” (OP9).