mine usually do yes - sometimes not, but to be fair mine don't get as dirty! lol. i'm not exactly a mother who cares too much - more a view of oh well it will wash, than sit there and don't go in the garden type!.
if just your ds's clothes and not yours, maybe they are clean just marked where he's spilt something or played or trouser hems dragged on floor? I never think my lo's clothes look as clean as ours but its not because they aren't clean iyswim, just she's marked them with something.
btw, she's not a total scruff, just not overly careful about spilling or running in puddles or lying down on wet grass n stuff
Spandex, I never use 30 for lo's stuff, never comes out very well or on quick wash. Wash on a 40 n they should be ok. and, i find co-op green household soap is good for stains like spilled spaghetti or juice or whatever else, works better than vanish which is ridiculously expensive imo.