These days 27.5" and 29" is the standard. It’s quite hard finding forks, tires etc for 26".
I bought a enduro/downhill bike for my son, and wouldn’t have spent that money if it wasn’t possible to covert it from 24" to 26", which is a must for these kind of child bikes.
I haven’t seen “it’s always sunny in philadelphia”, but I still got the reference…