i mean, work experience isn't a requirement to get into uni as far as i know??? but it does help (by which i mean, it's invaluable) if you want to get a job whilst at uni. i would recommend charity shops bc they're always hiring. they don't pay, but it's good to use as a ref to get to paid retail jobs. if you want something specific for your course, then it would depend what you're interested in. criminal psychology? psychotherapist? child psychology? mental illness? have a look for jobs in health/social care, but you're unlikely to find anything while so young that you can fit around a school/uni work schedule.
sorry i can't help more!
p.t.