@hembrow ooooooh I just looked at your profile!

we have a 24" Cannondale Quick with zero attachment points for any accessories. The detachable rear mudflap we have is from planetbike, and it's probably better suited for an adult's bike (not a kid who's not likely to notice if it's gone sideways).

Maybe not a problem that can be solved from the EU but I'd be beyond grateful for suggestions.

@DrTCombs It's a bit daft that they make frames without mounting points for what are supposed to be practical bicycles, but you can work around it. Those clip on mudguard things never work (IME).

You need three fitting points for a normal front mudguard (the one that's most important to keep your feet dry). The photos I've found suggest that there is already a hole through the fork crown on the bike, so that's one of the three. The other two could be made with p-clips from your local DIY store, sized to fit snugly around the fork fairly close to the axle.

At the rear you can probably also use p-clips on the seat stays, placed fairly low near the axle. I can't see a any photos which make it obvious what you'd need at the mid point. But I think with a few p-clips you can probably fit any mudguard of the correct size to the front and rear.

@DrTCombs @hembrow I use these on my gravel bike. They sit quite well. Don't know if they will fit your daughter's bike, but the attachment system is solid and flexible. Maybe it can be repurposed.
https://www.sks-germany.com/en/products/speedrocker/