I started my 6yr old on vyvanse (lisdexamfetamine) today (10mg), teachers said she was very irriatble, sad, even banged head purposely - does it take a few days?

Close follow-up: Stimulants, including Vyvanse, Adderall, Focalin, (dexmethylphenidate) Ritalin/Concerta, all work very quickly in the body. While it may take time and trial and error to find the right dose for a child or adult, if multiple people observe concerning behavioral side effects, it is important to alert the prescribing physician immediately.

Yes: Vyvanse (lisdexamfetamine) is a psycho-stimulant. It changes the brain chemistry. It will probably take him a few days to get used to it. However, get details about why he is doing these things and convey this to his doctor.