Hey!
Noob here and was wondering if there are any issues converting the 26 inch wheels to 24 inch on a mtn bike. Disc brakes seems would fit ok but now sure of the der's.
Thanks!

I think you'd be better off buying an MTB designed around 24" wheels, if you have that option. Putting those on a bike designed for 26" wheels will result in a much lower bottom bracket, which will increase the likelihood of your cranks striking the ground during turns- especially sharp ones at low speed, which people do a lot of in mountain biking. All your gears will end up being a lot lower too; you'll be able to pedal up anything, but you'll spin out at a much lower speed.

One thing I'm not familiar with is the axle width on 24s- anyone know if a 24" wheel will fit in dropouts designed for 26"?

no issues other than dropping the bike down- bottom bracket and crank clearance gets lower. the tire selection is much, much smaller (hah! hah!) and those smaller wheels tend to roll over stuff poorly/get stuck more in techy terrain.

so long as you swap both wheels, the rest of the geometry will remain the same. i guess the question is: why? what are you trying to achieve? that said, you can build some very strong and stiff wheels, though i don't think that outweighs the negatives.

if using disc brakes, no problems with the other stuff. a 135mm wide mountain hub will work with whichever rims you have laced to it, assuming that is your frame dropout width. mtb frames and forks are pretty standard, at least if only doing a QR setup.

Thanks for the input! I'm doing it to have the ability to bail quickly or jump onto the crossbar when my kid takes a dive off his bike. I'm short on the inseam and I just purchased a kona stuff for riding with the kids. No technical riding so the clearance wouldn't be an issue. I have a dual suspension higher end mtb for messin' about. I could swap sprockets on the 34's to help the gearing out I assume?
Thanks again!

You could install a larger big ring up front to correct the gearing, but bear in mind that the front der. can only handle a certain size difference between the largest and smallest ring. Some cheaper cranksets have the rings rivetted to the crank spider; in that case you will have to replace the whole crankset if you want taller gears. If you're mostly chasing the kids around on this bike, you may be OK with the gearset as it is.