How can I remove a paint splatter from the wall before my parents wake up??

For stubborn spots, wrap a rag around a plastic putty knife and scrape, exerting only light pressure. As a last resort, try applying a small amount of mineral spirits and wiping with a dry rag.
Answer:
if you have paint-stain remover, I recommend using that
(or, just put a sign or something to cover it)
it does depend on the type of paint, but it might come off with water/soap/scrubbing ?
or just like scratching it off/rubbing it with a towel; or scraping it off with a spoon or something
honestly, your best bet might just have to be being honest with your parents when they wake up. You can remind them that a) nobody got hurt ; b) you can paint it over
(or some other reasoning as to why it's not that bad)
update > rubbing alcohol works well for acrylic paint!!
i hope this helps, and good luck <3