My son's 24" bike came (2nd hand) w/ a 2-piece chainguard (that was aftermarket), one piece bracketed to the seat tube that hangs over the chainring (top only, not front or side), and one piece hanging over the straight run of chain from chainring to freewheel. Can't remember if that's also bracketed to the seattube or to the seatstay. They wobble, occasionally need to get off the bike and push them back where they belong. They would drive me crazy. But I'm glad he has them, for pants cuff protection purposes. Although this is the first week since like September he's been commuting in sneakers rather than wellies, so his cuffs have been safe to this point just via his footwear.

edit: I think there are just 2 periods of a month, maybe 6 weeks out of the year, in between pants-tucked-into-boots and shorts-and-sandals for him (and vice versa). That's when the chainguard is handy.