I would say that special needs clothing is real clothing as opposed to ABDL clothing which is more like a costume. For me, an ABDL onesie (for instance) could only be some sort of toy, while a special needs onesie is the real thing. Maybe this is a market for ABDL companies.
I actually bought a special needs onesie, in fact at time it was cheaper than the ABDL equivalent if I recall correctly, plus it can be considered as some sort of support (having a special needs child costs a fortune). I don’t wear it much though, but it’s amazing during the winter underneath regular clothes. Mine came from
Wonesie (Australian brand), a simple, plain white short sleeved.