I'm very fussy about laundry, I wash everything in sight. Until very recently I also ironed everything in sight, however I decided to stop doing most of the children's casual clothes to regain a bit of sanity.
I like my children to be clean when we leave the house. If that means changing them after breakfast then so be it... although I try to leave pyjamas on until after breakfast for this reason!
However once we're out I wouldn't change clothes just because there's a spot or two of food or dirt on them; it would have to be a pretty major milkshake spill or something like that. My youngest two are master and mistress of the #3, so the changes of clothes I take when we go out are usually reserved for poonami emergencies .
ETA I just realised I didn't actually answer your questions...
2: any of the above. If it was a friend who I knew to be clean I would assume something had gone wrong. If it was a stranger I'm not sure I would think to have an opinion.
3: I wouldn't interfere unless I suspected neglect.
May I ask why you're asking?